<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2021 Workiva-->
<!--r:f5aaccee-8a08-4235-8be7-35ee7da27639,g:98029ae1-e3c7-4f46-8449-14e2f4881ec2-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.bentley.com/role/Cover" xlink:type="simple" xlink:href="bsy-20210630.xsd#Cover"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/Cover" xlink:type="extended" id="ifc7c18828a764b46a7f465a51b38cfca_Cover">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_406638ac-028f-4abb-89b6-b22d51648a06" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_DocumentType_406638ac-028f-4abb-89b6-b22d51648a06" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_b307edb9-c7c0-4e52-acdf-994addd533b0" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_DocumentQuarterlyReport_b307edb9-c7c0-4e52-acdf-994addd533b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_273b8beb-4c45-4a7b-98a1-ca28a885d5f4" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_DocumentPeriodEndDate_273b8beb-4c45-4a7b-98a1-ca28a885d5f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_9566072f-38a5-4f73-8b79-09dc37d74641" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_DocumentTransitionReport_9566072f-38a5-4f73-8b79-09dc37d74641" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_2751c089-7a9e-4bf5-8c7b-82a88082bfd8" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_EntityFileNumber_2751c089-7a9e-4bf5-8c7b-82a88082bfd8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_fc4f48e7-19e5-422f-9a7d-073083b3aba7" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_EntityRegistrantName_fc4f48e7-19e5-422f-9a7d-073083b3aba7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_ecbccf68-6641-463d-ad51-76baf07ac469" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_EntityIncorporationStateCountryCode_ecbccf68-6641-463d-ad51-76baf07ac469" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_3013c232-67c5-4bf6-96ce-0215c98f5853" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_EntityTaxIdentificationNumber_3013c232-67c5-4bf6-96ce-0215c98f5853" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_51b1d719-3b14-4814-93fd-103b3ad0820f" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_EntityAddressAddressLine1_51b1d719-3b14-4814-93fd-103b3ad0820f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_76a80731-ace5-42c4-802d-ebbcbc5624c0" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_EntityAddressCityOrTown_76a80731-ace5-42c4-802d-ebbcbc5624c0" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_075dc102-a5c7-4a7c-80bd-76ccd675842b" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_EntityAddressStateOrProvince_075dc102-a5c7-4a7c-80bd-76ccd675842b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_356b0463-7551-45ed-b4fc-527901939a11" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_EntityAddressPostalZipCode_356b0463-7551-45ed-b4fc-527901939a11" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_65189713-a119-45c2-a113-b1741f4fc092" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_CityAreaCode_65189713-a119-45c2-a113-b1741f4fc092" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_4112486f-f082-4e4e-8b0d-4dfbc6ae181f" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_LocalPhoneNumber_4112486f-f082-4e4e-8b0d-4dfbc6ae181f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_de951f05-58e8-455e-b29e-a2e4f8322498" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_Security12bTitle_de951f05-58e8-455e-b29e-a2e4f8322498" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_0962dff3-4306-4e3a-a685-219b9508379a" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_TradingSymbol_0962dff3-4306-4e3a-a685-219b9508379a" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_8130dc8e-c88f-4ceb-a93a-dd7d589ee440" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_SecurityExchangeName_8130dc8e-c88f-4ceb-a93a-dd7d589ee440" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_3ccb6375-1a38-4839-9260-2febfad0e65a" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_EntityCurrentReportingStatus_3ccb6375-1a38-4839-9260-2febfad0e65a" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_4f06881b-12c8-4ebf-af95-e6763c7f39f4" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_EntityInteractiveDataCurrent_4f06881b-12c8-4ebf-af95-e6763c7f39f4" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_ac20c699-4cb0-45c6-b7ff-a45b90c4d542" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_EntityFilerCategory_ac20c699-4cb0-45c6-b7ff-a45b90c4d542" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_af44326a-d411-48c4-8b5d-800caeb203bf" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_EntitySmallBusiness_af44326a-d411-48c4-8b5d-800caeb203bf" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_d512e30f-0979-4ffd-a04e-f266c44f93f9" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_EntityEmergingGrowthCompany_d512e30f-0979-4ffd-a04e-f266c44f93f9" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityExTransitionPeriod_7a28fee1-cc92-4f00-a179-870ce2d0cd96" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityExTransitionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_EntityExTransitionPeriod_7a28fee1-cc92-4f00-a179-870ce2d0cd96" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_2a3cf070-a282-4531-bb1d-9cdff4d615ef" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_EntityShellCompany_2a3cf070-a282-4531-bb1d-9cdff4d615ef" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_fc8b9ea9-857d-4d02-9253-6095b554c63e" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_fc8b9ea9-857d-4d02-9253-6095b554c63e" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_46746534-71f3-4a67-a7e9-7dbe89820669" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_CurrentFiscalYearEndDate_46746534-71f3-4a67-a7e9-7dbe89820669" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_f2193e78-3084-4852-b6fe-30242d79d33d" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_EntityCentralIndexKey_f2193e78-3084-4852-b6fe-30242d79d33d" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_da819f77-9db2-44ef-aa12-ea9108b62db2" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_AmendmentFlag_da819f77-9db2-44ef-aa12-ea9108b62db2" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_ebd3d576-1d14-4b84-addf-9c815c50cd9b" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_DocumentFiscalPeriodFocus_ebd3d576-1d14-4b84-addf-9c815c50cd9b" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_bc1f14e3-dc96-4429-9582-9b0e61d64ad0" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_DocumentFiscalYearFocus_bc1f14e3-dc96-4429-9582-9b0e61d64ad0" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_d670018b-87ab-456e-9428-9651591c2506" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_36de4176-bf51-4bd4-9520-727c1643f7b9" xlink:to="loc_dei_DocumentInformationTable_d670018b-87ab-456e-9428-9651591c2506" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_5a3a0940-f0de-4326-bce8-5f7027dadf68" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_d670018b-87ab-456e-9428-9651591c2506" xlink:to="loc_us-gaap_StatementClassOfStockAxis_5a3a0940-f0de-4326-bce8-5f7027dadf68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_5a3a0940-f0de-4326-bce8-5f7027dadf68_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_5a3a0940-f0de-4326-bce8-5f7027dadf68" xlink:to="loc_us-gaap_ClassOfStockDomain_5a3a0940-f0de-4326-bce8-5f7027dadf68_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_3a9dfc73-8348-4ea3-abb0-9bea9792a9cf" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_5a3a0940-f0de-4326-bce8-5f7027dadf68" xlink:to="loc_us-gaap_ClassOfStockDomain_3a9dfc73-8348-4ea3-abb0-9bea9792a9cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_ac65fadb-4f8d-481c-b54c-e4bd3a434b9b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_3a9dfc73-8348-4ea3-abb0-9bea9792a9cf" xlink:to="loc_us-gaap_CommonClassAMember_ac65fadb-4f8d-481c-b54c-e4bd3a434b9b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_54b50e75-cfb8-4a57-996d-b6f8feef42e0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_3a9dfc73-8348-4ea3-abb0-9bea9792a9cf" xlink:to="loc_us-gaap_CommonClassBMember_54b50e75-cfb8-4a57-996d-b6f8feef42e0" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="simple" xlink:href="bsy-20210630.xsd#ConsolidatedBalanceSheetsParenthetical"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="extended" id="ifcd4dcd5554e4ce3810ddd0c44b94496_ConsolidatedBalanceSheetsParenthetical">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_02dbc10e-960b-439e-9af2-0f32f906f26a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_9ae225a4-c72f-4e7f-bbef-89d23db5fe8b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_02dbc10e-960b-439e-9af2-0f32f906f26a" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_9ae225a4-c72f-4e7f-bbef-89d23db5fe8b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_88893d5a-2474-481f-9011-79f8cc486cd2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_02dbc10e-960b-439e-9af2-0f32f906f26a" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_88893d5a-2474-481f-9011-79f8cc486cd2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_33fe928d-12c6-4232-abaa-0c30532816c4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_02dbc10e-960b-439e-9af2-0f32f906f26a" xlink:to="loc_us-gaap_PreferredStockSharesIssued_33fe928d-12c6-4232-abaa-0c30532816c4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_2fb21bf8-ba8f-4597-a45b-ebf368468e70" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_02dbc10e-960b-439e-9af2-0f32f906f26a" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_2fb21bf8-ba8f-4597-a45b-ebf368468e70" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_ea882560-0673-4cf1-9ab2-565783566005" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_02dbc10e-960b-439e-9af2-0f32f906f26a" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_ea882560-0673-4cf1-9ab2-565783566005" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_66b09493-4bdf-4415-926e-0bedcd9007cd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_02dbc10e-960b-439e-9af2-0f32f906f26a" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_66b09493-4bdf-4415-926e-0bedcd9007cd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_b7c08710-9a0d-41f7-a62d-d6b2eea92755" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_02dbc10e-960b-439e-9af2-0f32f906f26a" xlink:to="loc_us-gaap_CommonStockSharesIssued_b7c08710-9a0d-41f7-a62d-d6b2eea92755" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_9ae49391-4c90-404f-bc0e-4253fb537af3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_02dbc10e-960b-439e-9af2-0f32f906f26a" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_9ae49391-4c90-404f-bc0e-4253fb537af3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_25ea163e-9b03-480e-99e1-cc6e19a92b9b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_02dbc10e-960b-439e-9af2-0f32f906f26a" xlink:to="loc_us-gaap_StatementTable_25ea163e-9b03-480e-99e1-cc6e19a92b9b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_67737c99-8ec3-4547-8c4e-dd021bbf7002" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_25ea163e-9b03-480e-99e1-cc6e19a92b9b" xlink:to="loc_us-gaap_StatementClassOfStockAxis_67737c99-8ec3-4547-8c4e-dd021bbf7002" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_67737c99-8ec3-4547-8c4e-dd021bbf7002_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_67737c99-8ec3-4547-8c4e-dd021bbf7002" xlink:to="loc_us-gaap_ClassOfStockDomain_67737c99-8ec3-4547-8c4e-dd021bbf7002_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_ce4d535f-f11c-4983-a461-77315e97e2cc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_67737c99-8ec3-4547-8c4e-dd021bbf7002" xlink:to="loc_us-gaap_ClassOfStockDomain_ce4d535f-f11c-4983-a461-77315e97e2cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_560ed7f4-fe02-4826-ac3d-e2c3b080b822" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_ce4d535f-f11c-4983-a461-77315e97e2cc" xlink:to="loc_us-gaap_CommonClassAMember_560ed7f4-fe02-4826-ac3d-e2c3b080b822" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_2fbd0386-9f2b-4409-8b19-9a594f3d24d6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_ce4d535f-f11c-4983-a461-77315e97e2cc" xlink:to="loc_us-gaap_CommonClassBMember_2fbd0386-9f2b-4409-8b19-9a594f3d24d6" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/ConsolidatedStatementsofOperations" xlink:type="simple" xlink:href="bsy-20210630.xsd#ConsolidatedStatementsofOperations"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/ConsolidatedStatementsofOperations" xlink:type="extended" id="i361e91c72aa9400a9e10b3f47e83eb3a_ConsolidatedStatementsofOperations">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_9d498946-7e0e-4fce-b78a-608b65895b0f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_b95ede8a-935f-4d6f-a8d8-2cfe91578765" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d498946-7e0e-4fce-b78a-608b65895b0f" xlink:to="loc_us-gaap_RevenuesAbstract_b95ede8a-935f-4d6f-a8d8-2cfe91578765" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_237a6d85-fb1b-405d-ae2a-c5450a3b498a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_b95ede8a-935f-4d6f-a8d8-2cfe91578765" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_237a6d85-fb1b-405d-ae2a-c5450a3b498a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenueAbstract_fa927483-52c6-4b65-972d-b7417609b8a9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CostOfRevenueAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d498946-7e0e-4fce-b78a-608b65895b0f" xlink:to="loc_us-gaap_CostOfRevenueAbstract_fa927483-52c6-4b65-972d-b7417609b8a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenue_895829e8-a7a8-4caf-970a-4df8d0d80bc7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CostOfRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfRevenueAbstract_fa927483-52c6-4b65-972d-b7417609b8a9" xlink:to="loc_us-gaap_CostOfRevenue_895829e8-a7a8-4caf-970a-4df8d0d80bc7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossProfit_a86ff847-8437-4986-b99d-d0825d7aa0f8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GrossProfit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d498946-7e0e-4fce-b78a-608b65895b0f" xlink:to="loc_us-gaap_GrossProfit_a86ff847-8437-4986-b99d-d0825d7aa0f8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_a0df1f02-11c6-4f1e-99ae-a14de9194099" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d498946-7e0e-4fce-b78a-608b65895b0f" xlink:to="loc_us-gaap_OperatingExpensesAbstract_a0df1f02-11c6-4f1e-99ae-a14de9194099" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_14610bd2-87b5-4259-9aee-aebba94aa568" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_a0df1f02-11c6-4f1e-99ae-a14de9194099" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_14610bd2-87b5-4259-9aee-aebba94aa568" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpense_35acfd46-c697-47d6-acad-a394402878b3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SellingAndMarketingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_a0df1f02-11c6-4f1e-99ae-a14de9194099" xlink:to="loc_us-gaap_SellingAndMarketingExpense_35acfd46-c697-47d6-acad-a394402878b3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_7e8eba37-282f-402e-a9dd-2b4fce06dc13" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_a0df1f02-11c6-4f1e-99ae-a14de9194099" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_7e8eba37-282f-402e-a9dd-2b4fce06dc13" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_e349c5fe-b7ae-443f-8317-7d1b5160fd4c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_a0df1f02-11c6-4f1e-99ae-a14de9194099" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_e349c5fe-b7ae-443f-8317-7d1b5160fd4c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_bb0a4b1b-9cff-4f19-98c9-0f1c082cc4d0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_a0df1f02-11c6-4f1e-99ae-a14de9194099" xlink:to="loc_us-gaap_OperatingExpenses_bb0a4b1b-9cff-4f19-98c9-0f1c082cc4d0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_bb6919e9-5dda-4f9b-9fb1-4f099ef10ad5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d498946-7e0e-4fce-b78a-608b65895b0f" xlink:to="loc_us-gaap_OperatingIncomeLoss_bb6919e9-5dda-4f9b-9fb1-4f099ef10ad5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNonoperatingNet_891f9dff-5b3f-4e97-b0d6-7007cc67baad" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestIncomeExpenseNonoperatingNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d498946-7e0e-4fce-b78a-608b65895b0f" xlink:to="loc_us-gaap_InterestIncomeExpenseNonoperatingNet_891f9dff-5b3f-4e97-b0d6-7007cc67baad" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_e6d989be-de95-4d6f-996f-718787618eb5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d498946-7e0e-4fce-b78a-608b65895b0f" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_e6d989be-de95-4d6f-996f-718787618eb5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_87637b0e-29b0-45ed-a61c-1e9bff6a92a0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d498946-7e0e-4fce-b78a-608b65895b0f" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_87637b0e-29b0-45ed-a61c-1e9bff6a92a0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_5eeb7040-d148-4ac8-abc3-6fd541cbd36d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d498946-7e0e-4fce-b78a-608b65895b0f" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_5eeb7040-d148-4ac8-abc3-6fd541cbd36d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_6b5b02d4-2b54-49a9-be5e-d13d1510e16a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d498946-7e0e-4fce-b78a-608b65895b0f" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_6b5b02d4-2b54-49a9-be5e-d13d1510e16a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_1d1aac2b-9773-413d-b4d0-9a63c426af75" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d498946-7e0e-4fce-b78a-608b65895b0f" xlink:to="loc_us-gaap_NetIncomeLoss_1d1aac2b-9773-413d-b4d0-9a63c426af75" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesBasic_348bd5b3-1286-4b5c-890f-9631ccd6c85a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d498946-7e0e-4fce-b78a-608b65895b0f" xlink:to="loc_us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesBasic_348bd5b3-1286-4b5c-890f-9631ccd6c85a" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_7f4a1f40-240f-411b-a974-5f40ca48d1af" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d498946-7e0e-4fce-b78a-608b65895b0f" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_7f4a1f40-240f-411b-a974-5f40ca48d1af" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareAbstract_84df54d3-8bf7-4d63-9d0c-282e5cc2a780" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EarningsPerShareAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d498946-7e0e-4fce-b78a-608b65895b0f" xlink:to="loc_us-gaap_EarningsPerShareAbstract_84df54d3-8bf7-4d63-9d0c-282e5cc2a780" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_1a2bd8e9-10c2-4f6d-a895-84ff6cd8782c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_84df54d3-8bf7-4d63-9d0c-282e5cc2a780" xlink:to="loc_us-gaap_EarningsPerShareBasic_1a2bd8e9-10c2-4f6d-a895-84ff6cd8782c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_f4f5a84d-b56a-4fe1-8b13-336bda2c200d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_84df54d3-8bf7-4d63-9d0c-282e5cc2a780" xlink:to="loc_us-gaap_EarningsPerShareDiluted_f4f5a84d-b56a-4fe1-8b13-336bda2c200d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_389b3ba7-efa5-4cfb-8d9b-50d5ca4044bd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_84df54d3-8bf7-4d63-9d0c-282e5cc2a780" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_389b3ba7-efa5-4cfb-8d9b-50d5ca4044bd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_3e587347-3f6d-4ec7-a560-a1a35c51f4b9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_84df54d3-8bf7-4d63-9d0c-282e5cc2a780" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_3e587347-3f6d-4ec7-a560-a1a35c51f4b9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_8c311596-2c23-4449-96b4-13bf38bc93be" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_9d498946-7e0e-4fce-b78a-608b65895b0f" xlink:to="loc_us-gaap_StatementTable_8c311596-2c23-4449-96b4-13bf38bc93be" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_ed39d961-4c52-48ed-8a89-fb203d4b1477" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_8c311596-2c23-4449-96b4-13bf38bc93be" xlink:to="loc_srt_ProductOrServiceAxis_ed39d961-4c52-48ed-8a89-fb203d4b1477" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_ed39d961-4c52-48ed-8a89-fb203d4b1477_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_ed39d961-4c52-48ed-8a89-fb203d4b1477" xlink:to="loc_srt_ProductsAndServicesDomain_ed39d961-4c52-48ed-8a89-fb203d4b1477_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_80c7b979-164e-4370-a8fa-2c11f821c77f" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_ed39d961-4c52-48ed-8a89-fb203d4b1477" xlink:to="loc_srt_ProductsAndServicesDomain_80c7b979-164e-4370-a8fa-2c11f821c77f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_SubscriptionsAndLicensesMember_0d2713f8-31f3-43e4-90fe-d7b60c7abcf0" xlink:href="bsy-20210630.xsd#bsy_SubscriptionsAndLicensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_80c7b979-164e-4370-a8fa-2c11f821c77f" xlink:to="loc_bsy_SubscriptionsAndLicensesMember_0d2713f8-31f3-43e4-90fe-d7b60c7abcf0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubscriptionAndCirculationMember_b291edf3-85cf-4c7c-8a6a-f891232a9743" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubscriptionAndCirculationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_SubscriptionsAndLicensesMember_0d2713f8-31f3-43e4-90fe-d7b60c7abcf0" xlink:to="loc_us-gaap_SubscriptionAndCirculationMember_b291edf3-85cf-4c7c-8a6a-f891232a9743" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_PerpetualLicensesMember_e6f8c524-b522-4da3-b6d4-0b30eb3f67ab" xlink:href="bsy-20210630.xsd#bsy_PerpetualLicensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_SubscriptionsAndLicensesMember_0d2713f8-31f3-43e4-90fe-d7b60c7abcf0" xlink:to="loc_bsy_PerpetualLicensesMember_e6f8c524-b522-4da3-b6d4-0b30eb3f67ab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceMember_d45ae297-fa9a-4704-be11-09ea6d216d8b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_80c7b979-164e-4370-a8fa-2c11f821c77f" xlink:to="loc_us-gaap_ServiceMember_d45ae297-fa9a-4704-be11-09ea6d216d8b" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/ConsolidatedStatementsofStockholdersEquity" xlink:type="simple" xlink:href="bsy-20210630.xsd#ConsolidatedStatementsofStockholdersEquity"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/ConsolidatedStatementsofStockholdersEquity" xlink:type="extended" id="i7f966dffdd334aa89da0078684590ce1_ConsolidatedStatementsofStockholdersEquity">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_cef3ac89-bd2d-4575-bfcc-a0c121de03f2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_cef3ac89-bd2d-4575-bfcc-a0c121de03f2" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_440999ae-2172-41f6-a056-dfdc17911479" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_440999ae-2172-41f6-a056-dfdc17911479" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_4d2c0d5e-e3d8-4d1e-ab58-0987f7555a4b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_StockholdersEquity_4d2c0d5e-e3d8-4d1e-ab58-0987f7555a4b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_3087435f-b9e3-44ec-ab54-0ba08b565405" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_NetIncomeLoss_3087435f-b9e3-44ec-ab54-0ba08b565405" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_ad77b42f-2ae3-4f4e-9afc-311a14c41281" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_ad77b42f-2ae3-4f4e-9afc-311a14c41281" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_71cff1f8-d4f6-44e4-bd3d-d691b06321d3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_71cff1f8-d4f6-44e4-bd3d-d691b06321d3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_636e0b5c-eac5-4b35-bea3-abdfdd71e62f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_636e0b5c-eac5-4b35-bea3-abdfdd71e62f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_AdjustmentsToAdditionalPaidInCapitalPurchaseOfCappedCallOptions_6a3063a6-e6a6-47c7-8f31-d1b90c729599" xlink:href="bsy-20210630.xsd#bsy_AdjustmentsToAdditionalPaidInCapitalPurchaseOfCappedCallOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_bsy_AdjustmentsToAdditionalPaidInCapitalPurchaseOfCappedCallOptions_6a3063a6-e6a6-47c7-8f31-d1b90c729599" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Dividends_13e8d4c5-2988-4ea1-9da9-b98d7d5e05a6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Dividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_Dividends_13e8d4c5-2988-4ea1-9da9-b98d7d5e05a6" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_35118caa-b0b4-41f9-842d-efd432fbb8b3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_35118caa-b0b4-41f9-842d-efd432fbb8b3" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_9e1d85b7-38b3-4c45-8276-5014441ebc8b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_9e1d85b7-38b3-4c45-8276-5014441ebc8b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_StockIssuedDuringPeriodSharesDeferredCompensationPlan_a3ca35af-20f3-4e8b-ac46-66acaaaa864d" xlink:href="bsy-20210630.xsd#bsy_StockIssuedDuringPeriodSharesDeferredCompensationPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_bsy_StockIssuedDuringPeriodSharesDeferredCompensationPlan_a3ca35af-20f3-4e8b-ac46-66acaaaa864d" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_StockIssuedDuringPeriodValueDeferredCompensationPlan_338e56ef-fe5e-4cbb-9c7f-a5b9a72d9b7e" xlink:href="bsy-20210630.xsd#bsy_StockIssuedDuringPeriodValueDeferredCompensationPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_bsy_StockIssuedDuringPeriodValueDeferredCompensationPlan_338e56ef-fe5e-4cbb-9c7f-a5b9a72d9b7e" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_AdjustmentsToAdditionalPaidInCapitalDeferredCompensationPlanVoluntaryContributions_ae315ae5-d550-47de-ab6f-43be082fcad7" xlink:href="bsy-20210630.xsd#bsy_AdjustmentsToAdditionalPaidInCapitalDeferredCompensationPlanVoluntaryContributions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_bsy_AdjustmentsToAdditionalPaidInCapitalDeferredCompensationPlanVoluntaryContributions_ae315ae5-d550-47de-ab6f-43be082fcad7" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_e251fc7f-e9a6-4331-80fb-0fb5a6a6c404" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesIssuedForServices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_e251fc7f-e9a6-4331-80fb-0fb5a6a6c404" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueIssuedForServices_54ade00e-4224-4d89-9f51-f2684ac672bb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueIssuedForServices"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueIssuedForServices_54ade00e-4224-4d89-9f51-f2684ac672bb" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_253ead5c-c4bc-40ba-aad8-b1c42b6ad33e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_253ead5c-c4bc-40ba-aad8-b1c42b6ad33e" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_2f003663-55c9-4831-ace0-bc40ba5392ad" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_2f003663-55c9-4831-ace0-bc40ba5392ad" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_CommonStockPurchaseAgreementNet_3b843f82-0f9b-4f66-9bb8-e12e9e900b55" xlink:href="bsy-20210630.xsd#bsy_CommonStockPurchaseAgreementNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_bsy_CommonStockPurchaseAgreementNet_3b843f82-0f9b-4f66-9bb8-e12e9e900b55" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromRepaymentOfLoansToPurchaseCommonStock_6366d115-0a26-49e0-8975-cd6ce9b32b45" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromRepaymentOfLoansToPurchaseCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_ProceedsFromRepaymentOfLoansToPurchaseCommonStock_6366d115-0a26-49e0-8975-cd6ce9b32b45" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_35150134-e0f5-4d12-8f7a-8c28a96c91d7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_35150134-e0f5-4d12-8f7a-8c28a96c91d7" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_1d3a6858-f9bf-44e0-9487-98b44c41e994" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_1d3a6858-f9bf-44e0-9487-98b44c41e994" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestGrantedNumber_79f4f792-1cde-4279-a268-0e78360b4b99" xlink:href="bsy-20210630.xsd#bsy_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestGrantedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_bsy_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestGrantedNumber_79f4f792-1cde-4279-a268-0e78360b4b99" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestGrantedValue_34156ca3-739f-41fe-8e7c-834897dc7ea1" xlink:href="bsy-20210630.xsd#bsy_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestGrantedValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_bsy_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestGrantedValue_34156ca3-739f-41fe-8e7c-834897dc7ea1" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_c34fc9ba-ddb2-49e7-8e1e-f995f9fae1af" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_c34fc9ba-ddb2-49e7-8e1e-f995f9fae1af" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_f5ebeba9-0b37-4730-ba81-0ac54e6a98db" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_f5ebeba9-0b37-4730-ba81-0ac54e6a98db" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_95ae6913-9af6-415a-a677-e753005c444d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_0b17d223-afa5-42fb-8eb7-0a7424c3d445" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_95ae6913-9af6-415a-a677-e753005c444d" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_afcc0333-cbcd-4a20-b042-162c9126fd2d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_35c66ea1-b378-43a7-947c-662846e52cf4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_0af906bb-6df8-4d44-912c-ca66145086e4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_cef3ac89-bd2d-4575-bfcc-a0c121de03f2" xlink:to="loc_us-gaap_StatementTable_0af906bb-6df8-4d44-912c-ca66145086e4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_a4c4fc16-bed4-4b49-8f1d-87275c9959e0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_0af906bb-6df8-4d44-912c-ca66145086e4" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_a4c4fc16-bed4-4b49-8f1d-87275c9959e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_a4c4fc16-bed4-4b49-8f1d-87275c9959e0_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_a4c4fc16-bed4-4b49-8f1d-87275c9959e0" xlink:to="loc_us-gaap_EquityComponentDomain_a4c4fc16-bed4-4b49-8f1d-87275c9959e0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_f14eae58-0970-4099-baa6-a1afa9d89418" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_a4c4fc16-bed4-4b49-8f1d-87275c9959e0" xlink:to="loc_us-gaap_EquityComponentDomain_f14eae58-0970-4099-baa6-a1afa9d89418" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_cae97d13-bf32-46dd-9318-aa060412b210" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f14eae58-0970-4099-baa6-a1afa9d89418" xlink:to="loc_us-gaap_CommonStockMember_cae97d13-bf32-46dd-9318-aa060412b210" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_ae405417-7261-43a8-92e1-93a953134c1e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f14eae58-0970-4099-baa6-a1afa9d89418" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_ae405417-7261-43a8-92e1-93a953134c1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_3ac74648-cc8a-4f6e-84c2-c44f6b51fcdc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f14eae58-0970-4099-baa6-a1afa9d89418" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_3ac74648-cc8a-4f6e-84c2-c44f6b51fcdc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_19761683-1f1f-4ff2-9126-515f02556704" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_f14eae58-0970-4099-baa6-a1afa9d89418" xlink:to="loc_us-gaap_RetainedEarningsMember_19761683-1f1f-4ff2-9126-515f02556704" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/BasisofPresentationNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#BasisofPresentationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/BasisofPresentationNarrativeDetails" xlink:type="extended" id="i09acfeb9ed4940e6ac5cc6d7e0c9976a_BasisofPresentationNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockLineItems_f31b034c-7de4-4364-be73-2ac09cb74292" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsidiarySaleOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_bacc016e-e0ad-4ff9-95fb-b9a3d8b13aac" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_f31b034c-7de4-4364-be73-2ac09cb74292" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_bacc016e-e0ad-4ff9-95fb-b9a3d8b13aac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_c349360c-4491-4848-9d04-d1e20beb8ea6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_f31b034c-7de4-4364-be73-2ac09cb74292" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_c349360c-4491-4848-9d04-d1e20beb8ea6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_0d2c2f20-a87c-4800-bcea-8956ec8adfeb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_f31b034c-7de4-4364-be73-2ac09cb74292" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_0d2c2f20-a87c-4800-bcea-8956ec8adfeb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_216626af-942c-4d81-937f-ca6b5d32dd36" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_f31b034c-7de4-4364-be73-2ac09cb74292" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_216626af-942c-4d81-937f-ca6b5d32dd36" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDebtIssuanceCosts_0d2a5eff-1c68-46eb-9fe6-ebb67f1ab15f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsOfDebtIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_f31b034c-7de4-4364-be73-2ac09cb74292" xlink:to="loc_us-gaap_PaymentsOfDebtIssuanceCosts_0d2a5eff-1c68-46eb-9fe6-ebb67f1ab15f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_498bac6a-727d-4d2c-a7eb-11148e641968" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_f31b034c-7de4-4364-be73-2ac09cb74292" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_498bac6a-727d-4d2c-a7eb-11148e641968" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_76901cf0-01cf-4adf-a5e8-cadd49485db3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SaleOfStockPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_f31b034c-7de4-4364-be73-2ac09cb74292" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_76901cf0-01cf-4adf-a5e8-cadd49485db3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_f0e682a6-0d1c-447d-9047-c5dd6d359938" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_f31b034c-7de4-4364-be73-2ac09cb74292" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_f0e682a6-0d1c-447d-9047-c5dd6d359938" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_StockIssuanceCosts_79d6d209-40a0-4a43-9e66-90ac13d4ad42" xlink:href="bsy-20210630.xsd#bsy_StockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_f31b034c-7de4-4364-be73-2ac09cb74292" xlink:to="loc_bsy_StockIssuanceCosts_79d6d209-40a0-4a43-9e66-90ac13d4ad42" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_59f9eae4-7abb-43bc-9255-03ca9414aa52" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsidiarySaleOfStockLineItems_f31b034c-7de4-4364-be73-2ac09cb74292" xlink:to="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_59f9eae4-7abb-43bc-9255-03ca9414aa52" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_d00bbe97-36a0-4320-a924-43767af82c28" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_59f9eae4-7abb-43bc-9255-03ca9414aa52" xlink:to="loc_us-gaap_DebtInstrumentAxis_d00bbe97-36a0-4320-a924-43767af82c28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_d00bbe97-36a0-4320-a924-43767af82c28_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_d00bbe97-36a0-4320-a924-43767af82c28" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_d00bbe97-36a0-4320-a924-43767af82c28_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_5f029622-1fe0-456e-b309-46c424afb900" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_d00bbe97-36a0-4320-a924-43767af82c28" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_5f029622-1fe0-456e-b309-46c424afb900" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentySixNotesMember_458981ef-bbaa-438f-9af8-5f829ea1a7ea" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentySixNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_5f029622-1fe0-456e-b309-46c424afb900" xlink:to="loc_bsy_TwoThousandTwentySixNotesMember_458981ef-bbaa-438f-9af8-5f829ea1a7ea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentySevenNotesMember_0193a859-89b0-4214-a963-196ca88e7d6d" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentySevenNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_5f029622-1fe0-456e-b309-46c424afb900" xlink:to="loc_bsy_TwoThousandTwentySevenNotesMember_0193a859-89b0-4214-a963-196ca88e7d6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_b2f2cda5-a89b-4f1a-81b0-bed422cd50f0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_59f9eae4-7abb-43bc-9255-03ca9414aa52" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_b2f2cda5-a89b-4f1a-81b0-bed422cd50f0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_b2f2cda5-a89b-4f1a-81b0-bed422cd50f0_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_b2f2cda5-a89b-4f1a-81b0-bed422cd50f0" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_b2f2cda5-a89b-4f1a-81b0-bed422cd50f0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_6e508668-816a-488b-be8d-d43c5e516b73" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_b2f2cda5-a89b-4f1a-81b0-bed422cd50f0" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_6e508668-816a-488b-be8d-d43c5e516b73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_d746f98d-6fd3-4fef-a9df-0d97ee1a0e14" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_6e508668-816a-488b-be8d-d43c5e516b73" xlink:to="loc_us-gaap_ConvertibleDebtMember_d746f98d-6fd3-4fef-a9df-0d97ee1a0e14" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_62330528-1e3e-44e1-8daf-fdcb6e0172fa" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_59f9eae4-7abb-43bc-9255-03ca9414aa52" xlink:to="loc_us-gaap_StatementClassOfStockAxis_62330528-1e3e-44e1-8daf-fdcb6e0172fa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_62330528-1e3e-44e1-8daf-fdcb6e0172fa_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_62330528-1e3e-44e1-8daf-fdcb6e0172fa" xlink:to="loc_us-gaap_ClassOfStockDomain_62330528-1e3e-44e1-8daf-fdcb6e0172fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_9741edee-4773-41b8-a6f8-30310a4ba238" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_62330528-1e3e-44e1-8daf-fdcb6e0172fa" xlink:to="loc_us-gaap_ClassOfStockDomain_9741edee-4773-41b8-a6f8-30310a4ba238" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_2fb5fdfc-a709-495d-b15f-49989f335bdf" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_9741edee-4773-41b8-a6f8-30310a4ba238" xlink:to="loc_us-gaap_CommonClassBMember_2fb5fdfc-a709-495d-b15f-49989f335bdf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_4e74caef-5645-40e5-85a7-fdf935b53e53" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_59f9eae4-7abb-43bc-9255-03ca9414aa52" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_4e74caef-5645-40e5-85a7-fdf935b53e53" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_4e74caef-5645-40e5-85a7-fdf935b53e53_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_4e74caef-5645-40e5-85a7-fdf935b53e53" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_4e74caef-5645-40e5-85a7-fdf935b53e53_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_f2f4bdef-9724-453d-b79c-e3c09172a971" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_4e74caef-5645-40e5-85a7-fdf935b53e53" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_f2f4bdef-9724-453d-b79c-e3c09172a971" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_PublicStockOfferingSharesFromExistingShareholdersMember_8a6bfd20-a482-4449-af5f-8ff61f304046" xlink:href="bsy-20210630.xsd#bsy_PublicStockOfferingSharesFromExistingShareholdersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_f2f4bdef-9724-453d-b79c-e3c09172a971" xlink:to="loc_bsy_PublicStockOfferingSharesFromExistingShareholdersMember_8a6bfd20-a482-4449-af5f-8ff61f304046" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_FollowOnOfferingMember_3893955f-4fbe-479f-af09-36653998b808" xlink:href="bsy-20210630.xsd#bsy_FollowOnOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_f2f4bdef-9724-453d-b79c-e3c09172a971" xlink:to="loc_bsy_FollowOnOfferingMember_3893955f-4fbe-479f-af09-36653998b808" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_FollowOnOfferingSoldByCompanyMember_811e4c48-1acc-4fc7-94c4-d195bdc85948" xlink:href="bsy-20210630.xsd#bsy_FollowOnOfferingSoldByCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_f2f4bdef-9724-453d-b79c-e3c09172a971" xlink:to="loc_bsy_FollowOnOfferingSoldByCompanyMember_811e4c48-1acc-4fc7-94c4-d195bdc85948" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_FollowOnOfferingExerciseByUnderwritersMember_55151c7a-e85c-471d-8d23-48d52bf82bb1" xlink:href="bsy-20210630.xsd#bsy_FollowOnOfferingExerciseByUnderwritersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_f2f4bdef-9724-453d-b79c-e3c09172a971" xlink:to="loc_bsy_FollowOnOfferingExerciseByUnderwritersMember_55151c7a-e85c-471d-8d23-48d52bf82bb1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_FollowOnOfferingSharesFromExistingShareholdersMember_b6238b11-ada2-4a77-8810-b71f57218fd3" xlink:href="bsy-20210630.xsd#bsy_FollowOnOfferingSharesFromExistingShareholdersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_f2f4bdef-9724-453d-b79c-e3c09172a971" xlink:to="loc_bsy_FollowOnOfferingSharesFromExistingShareholdersMember_b6238b11-ada2-4a77-8810-b71f57218fd3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_be546bd6-d28e-4b4f-9003-06dc93bf4db1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable_59f9eae4-7abb-43bc-9255-03ca9414aa52" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_be546bd6-d28e-4b4f-9003-06dc93bf4db1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_be546bd6-d28e-4b4f-9003-06dc93bf4db1_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_be546bd6-d28e-4b4f-9003-06dc93bf4db1" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_be546bd6-d28e-4b4f-9003-06dc93bf4db1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_33b6ea4d-ad9a-4540-83df-6941904b39dd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_be546bd6-d28e-4b4f-9003-06dc93bf4db1" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_33b6ea4d-ad9a-4540-83df-6941904b39dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_SeequentMember_43ab2106-d140-4532-9fc9-95c9e4c56b16" xlink:href="bsy-20210630.xsd#bsy_SeequentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_33b6ea4d-ad9a-4540-83df-6941904b39dd" xlink:to="loc_bsy_SeequentMember_43ab2106-d140-4532-9fc9-95c9e4c56b16" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/RevenuefromContractswithCustomerNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#RevenuefromContractswithCustomerNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/RevenuefromContractswithCustomerNarrativeDetails" xlink:type="extended" id="ib4d4b0c850d04a748b73173f409323d1_RevenuefromContractswithCustomerNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_bd685d12-806f-4f5b-8254-74d2104b268a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiability_391866f2-7b57-4712-aacc-4f8b6b88a82f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ContractWithCustomerLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_bd685d12-806f-4f5b-8254-74d2104b268a" xlink:to="loc_us-gaap_ContractWithCustomerLiability_391866f2-7b57-4712-aacc-4f8b6b88a82f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostImpairmentLoss_e2366ea0-b9d3-4497-ac0d-f7d3186470b4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CapitalizedContractCostImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_bd685d12-806f-4f5b-8254-74d2104b268a" xlink:to="loc_us-gaap_CapitalizedContractCostImpairmentLoss_e2366ea0-b9d3-4497-ac0d-f7d3186470b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_5fd20053-4ea5-49da-9245-64090e450f95" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_bd685d12-806f-4f5b-8254-74d2104b268a" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_5fd20053-4ea5-49da-9245-64090e450f95" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_ContractWithCustomerLiabilityAdditions_08598883-eb05-4305-99ea-eabfea167700" xlink:href="bsy-20210630.xsd#bsy_ContractWithCustomerLiabilityAdditions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_bd685d12-806f-4f5b-8254-74d2104b268a" xlink:to="loc_bsy_ContractWithCustomerLiabilityAdditions_08598883-eb05-4305-99ea-eabfea167700" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_5f4c2774-552b-43d9-b8cb-20206627f766" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_bd685d12-806f-4f5b-8254-74d2104b268a" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_5f4c2774-552b-43d9-b8cb-20206627f766" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_ac4dab82-0b63-4bea-8ec7-1572bf7698c4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_bd685d12-806f-4f5b-8254-74d2104b268a" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_ac4dab82-0b63-4bea-8ec7-1572bf7698c4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_ddbe3982-b88f-4af4-ab00-d290623e8fa7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_bd685d12-806f-4f5b-8254-74d2104b268a" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_ddbe3982-b88f-4af4-ab00-d290623e8fa7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_a741111d-230f-48b7-940d-725559193d78" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_ddbe3982-b88f-4af4-ab00-d290623e8fa7" xlink:to="loc_srt_ProductOrServiceAxis_a741111d-230f-48b7-940d-725559193d78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_a741111d-230f-48b7-940d-725559193d78_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_a741111d-230f-48b7-940d-725559193d78" xlink:to="loc_srt_ProductsAndServicesDomain_a741111d-230f-48b7-940d-725559193d78_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_dc89cff9-0701-447d-9b28-089ece8ac19c" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_a741111d-230f-48b7-940d-725559193d78" xlink:to="loc_srt_ProductsAndServicesDomain_dc89cff9-0701-447d-9b28-089ece8ac19c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_PortfolioBalancingExchangeRightsMember_2e78bcdb-851b-43c5-9179-b1933b74d3b4" xlink:href="bsy-20210630.xsd#bsy_PortfolioBalancingExchangeRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_dc89cff9-0701-447d-9b28-089ece8ac19c" xlink:to="loc_bsy_PortfolioBalancingExchangeRightsMember_2e78bcdb-851b-43c5-9179-b1933b74d3b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicenseMember_86b916f8-ac29-45e3-a056-af47cb9ed4ef" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_dc89cff9-0701-447d-9b28-089ece8ac19c" xlink:to="loc_us-gaap_LicenseMember_86b916f8-ac29-45e3-a056-af47cb9ed4ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TermLicensesMember_2af15d93-915c-4172-bd9a-8bc4935d3295" xlink:href="bsy-20210630.xsd#bsy_TermLicensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LicenseMember_86b916f8-ac29-45e3-a056-af47cb9ed4ef" xlink:to="loc_bsy_TermLicensesMember_2af15d93-915c-4172-bd9a-8bc4935d3295" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_4a9c2e71-9935-48fd-878f-86586fb2b37f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_ddbe3982-b88f-4af4-ab00-d290623e8fa7" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_4a9c2e71-9935-48fd-878f-86586fb2b37f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_4a9c2e71-9935-48fd-878f-86586fb2b37f_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_4a9c2e71-9935-48fd-878f-86586fb2b37f" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_4a9c2e71-9935-48fd-878f-86586fb2b37f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_c11bade1-d719-40ac-acdf-2c3d3d74b65c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_4a9c2e71-9935-48fd-878f-86586fb2b37f" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_c11bade1-d719-40ac-acdf-2c3d3d74b65c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_4e3d89ec-84bb-4be8-be4f-b1fc74e337ce" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_c11bade1-d719-40ac-acdf-2c3d3d74b65c" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_4e3d89ec-84bb-4be8-be4f-b1fc74e337ce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_c155a9bc-e73d-45c1-a4a6-e5ac566c4ea8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_ddbe3982-b88f-4af4-ab00-d290623e8fa7" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_c155a9bc-e73d-45c1-a4a6-e5ac566c4ea8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_c155a9bc-e73d-45c1-a4a6-e5ac566c4ea8_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_c155a9bc-e73d-45c1-a4a6-e5ac566c4ea8" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_c155a9bc-e73d-45c1-a4a6-e5ac566c4ea8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_e0fe011c-fd8e-42a7-b669-e4745b00dd4b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_c155a9bc-e73d-45c1-a4a6-e5ac566c4ea8" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_e0fe011c-fd8e-42a7-b669-e4745b00dd4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_1386d984-d5f1-4706-bf44-e324d7d57d95" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_e0fe011c-fd8e-42a7-b669-e4745b00dd4b" xlink:to="loc_us-gaap_SalesRevenueNetMember_1386d984-d5f1-4706-bf44-e324d7d57d95" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_bd8ba2b0-c130-4e8b-af76-8a1fb80d80c2" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_ddbe3982-b88f-4af4-ab00-d290623e8fa7" xlink:to="loc_srt_MajorCustomersAxis_bd8ba2b0-c130-4e8b-af76-8a1fb80d80c2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_bd8ba2b0-c130-4e8b-af76-8a1fb80d80c2_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_bd8ba2b0-c130-4e8b-af76-8a1fb80d80c2" xlink:to="loc_srt_NameOfMajorCustomerDomain_bd8ba2b0-c130-4e8b-af76-8a1fb80d80c2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_ba20f008-95fc-4198-a104-0f9ffd6b8e57" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_bd8ba2b0-c130-4e8b-af76-8a1fb80d80c2" xlink:to="loc_srt_NameOfMajorCustomerDomain_ba20f008-95fc-4198-a104-0f9ffd6b8e57" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_ChannelPartnersMember_f05f8dc3-8978-42de-8dc2-310d638af23e" xlink:href="bsy-20210630.xsd#bsy_ChannelPartnersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_ba20f008-95fc-4198-a104-0f9ffd6b8e57" xlink:to="loc_bsy_ChannelPartnersMember_f05f8dc3-8978-42de-8dc2-310d638af23e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/RevenuefromContractswithCustomerPerformanceObligationDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#RevenuefromContractswithCustomerPerformanceObligationDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/RevenuefromContractswithCustomerPerformanceObligationDetails" xlink:type="extended" id="id5391867d76244a398ed82e1c83874c6_RevenuefromContractswithCustomerPerformanceObligationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_6f4c5279-4e84-48d8-864a-c027ae74bdf0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_521f880d-db48-432d-8213-56815032511d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_6f4c5279-4e84-48d8-864a-c027ae74bdf0" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_521f880d-db48-432d-8213-56815032511d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_c27ab4c3-e4a4-45cc-98bd-3a95cefaf37e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_6f4c5279-4e84-48d8-864a-c027ae74bdf0" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_c27ab4c3-e4a4-45cc-98bd-3a95cefaf37e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_040fd805-67b2-41c8-b43d-f502dfeac4a4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_6f4c5279-4e84-48d8-864a-c027ae74bdf0" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_040fd805-67b2-41c8-b43d-f502dfeac4a4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_1b5c18da-bd77-4b87-86c9-c3fc62d673ac" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_6f4c5279-4e84-48d8-864a-c027ae74bdf0" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_1b5c18da-bd77-4b87-86c9-c3fc62d673ac" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_21df337a-5349-45a7-b45f-83e509dc89b2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_1b5c18da-bd77-4b87-86c9-c3fc62d673ac" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_21df337a-5349-45a7-b45f-83e509dc89b2" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/RevenuefromContractswithCustomerPerformanceObligationDetails_1" xlink:type="simple" xlink:href="bsy-20210630.xsd#RevenuefromContractswithCustomerPerformanceObligationDetails_1"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/RevenuefromContractswithCustomerPerformanceObligationDetails_1" xlink:type="extended" id="i98f33279c08d4321b049ed3054d380ea_RevenuefromContractswithCustomerPerformanceObligationDetails_1">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_6f4c5279-4e84-48d8-864a-c027ae74bdf0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_521f880d-db48-432d-8213-56815032511d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_6f4c5279-4e84-48d8-864a-c027ae74bdf0" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_521f880d-db48-432d-8213-56815032511d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_c27ab4c3-e4a4-45cc-98bd-3a95cefaf37e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_6f4c5279-4e84-48d8-864a-c027ae74bdf0" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_c27ab4c3-e4a4-45cc-98bd-3a95cefaf37e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_040fd805-67b2-41c8-b43d-f502dfeac4a4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_6f4c5279-4e84-48d8-864a-c027ae74bdf0" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_040fd805-67b2-41c8-b43d-f502dfeac4a4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_1b5c18da-bd77-4b87-86c9-c3fc62d673ac" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_6f4c5279-4e84-48d8-864a-c027ae74bdf0" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_1b5c18da-bd77-4b87-86c9-c3fc62d673ac" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/RevenuefromContractswithCustomerScheduleofRevenueDisaggregationbyTypeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#RevenuefromContractswithCustomerScheduleofRevenueDisaggregationbyTypeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/RevenuefromContractswithCustomerScheduleofRevenueDisaggregationbyTypeDetails" xlink:type="extended" id="i137272aad5844887a00e6dab4e0a32bd_RevenuefromContractswithCustomerScheduleofRevenueDisaggregationbyTypeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_0474d395-d10a-4433-9d60-a55dc79de08e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_bfaf36f2-9d61-4680-9776-a989b3c30c71" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_0474d395-d10a-4433-9d60-a55dc79de08e" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_bfaf36f2-9d61-4680-9776-a989b3c30c71" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_cd1912e0-6916-4e8e-bc63-74bf436429f9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_0474d395-d10a-4433-9d60-a55dc79de08e" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_cd1912e0-6916-4e8e-bc63-74bf436429f9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_3ffae250-b39c-42ae-abc5-a985fa2cb256" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_cd1912e0-6916-4e8e-bc63-74bf436429f9" xlink:to="loc_srt_ProductOrServiceAxis_3ffae250-b39c-42ae-abc5-a985fa2cb256" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_3ffae250-b39c-42ae-abc5-a985fa2cb256_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_3ffae250-b39c-42ae-abc5-a985fa2cb256" xlink:to="loc_srt_ProductsAndServicesDomain_3ffae250-b39c-42ae-abc5-a985fa2cb256_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_7c2794ab-bd0c-40c6-8ca2-0c4d82e53c95" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_3ffae250-b39c-42ae-abc5-a985fa2cb256" xlink:to="loc_srt_ProductsAndServicesDomain_7c2794ab-bd0c-40c6-8ca2-0c4d82e53c95" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_SubscriptionsAndLicensesMember_ffdcfd38-515e-41ca-9c09-63c121ffd8a7" xlink:href="bsy-20210630.xsd#bsy_SubscriptionsAndLicensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_7c2794ab-bd0c-40c6-8ca2-0c4d82e53c95" xlink:to="loc_bsy_SubscriptionsAndLicensesMember_ffdcfd38-515e-41ca-9c09-63c121ffd8a7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubscriptionAndCirculationMember_0b11bb35-3a35-42f2-86a6-d6a4d75a73cc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubscriptionAndCirculationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_SubscriptionsAndLicensesMember_ffdcfd38-515e-41ca-9c09-63c121ffd8a7" xlink:to="loc_us-gaap_SubscriptionAndCirculationMember_0b11bb35-3a35-42f2-86a6-d6a4d75a73cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_SELECTSubscriptionsMember_755926ec-4521-4dd7-bf84-4e0e6c644e6e" xlink:href="bsy-20210630.xsd#bsy_SELECTSubscriptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubscriptionAndCirculationMember_0b11bb35-3a35-42f2-86a6-d6a4d75a73cc" xlink:to="loc_bsy_SELECTSubscriptionsMember_755926ec-4521-4dd7-bf84-4e0e6c644e6e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_EnterpriseLicenseSubscriptionsMember_2ff189ea-a537-477e-9b77-7a0b00bcee16" xlink:href="bsy-20210630.xsd#bsy_EnterpriseLicenseSubscriptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubscriptionAndCirculationMember_0b11bb35-3a35-42f2-86a6-d6a4d75a73cc" xlink:to="loc_bsy_EnterpriseLicenseSubscriptionsMember_2ff189ea-a537-477e-9b77-7a0b00bcee16" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_EnterpriseLicenseSubscriptionsE365SubscriptionsMember_ccfbaa40-9ec5-4849-8bfb-71374026cb08" xlink:href="bsy-20210630.xsd#bsy_EnterpriseLicenseSubscriptionsE365SubscriptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_EnterpriseLicenseSubscriptionsMember_2ff189ea-a537-477e-9b77-7a0b00bcee16" xlink:to="loc_bsy_EnterpriseLicenseSubscriptionsE365SubscriptionsMember_ccfbaa40-9ec5-4849-8bfb-71374026cb08" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TermLicenseSubscriptionsMember_f9112f0f-1111-4319-a1a5-774125dc96dc" xlink:href="bsy-20210630.xsd#bsy_TermLicenseSubscriptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubscriptionAndCirculationMember_0b11bb35-3a35-42f2-86a6-d6a4d75a73cc" xlink:to="loc_bsy_TermLicenseSubscriptionsMember_f9112f0f-1111-4319-a1a5-774125dc96dc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_PerpetualLicensesMember_53d8c36c-4ffe-4085-bc3e-ce6400c0ea2c" xlink:href="bsy-20210630.xsd#bsy_PerpetualLicensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_SubscriptionsAndLicensesMember_ffdcfd38-515e-41ca-9c09-63c121ffd8a7" xlink:to="loc_bsy_PerpetualLicensesMember_53d8c36c-4ffe-4085-bc3e-ce6400c0ea2c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceMember_3f99ef08-27ea-4249-9f62-8c021bc486c0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_7c2794ab-bd0c-40c6-8ca2-0c4d82e53c95" xlink:to="loc_us-gaap_ServiceMember_3f99ef08-27ea-4249-9f62-8c021bc486c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_ProfessionalServicesRecurringMember_799b262e-3d6f-4e2a-af33-1c0c8d7c0bf7" xlink:href="bsy-20210630.xsd#bsy_ProfessionalServicesRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ServiceMember_3f99ef08-27ea-4249-9f62-8c021bc486c0" xlink:to="loc_bsy_ProfessionalServicesRecurringMember_799b262e-3d6f-4e2a-af33-1c0c8d7c0bf7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_ProfessionalServicesOtherMember_2cf459f5-3da5-4f92-9f1e-51669ff851d6" xlink:href="bsy-20210630.xsd#bsy_ProfessionalServicesOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ServiceMember_3f99ef08-27ea-4249-9f62-8c021bc486c0" xlink:to="loc_bsy_ProfessionalServicesOtherMember_2cf459f5-3da5-4f92-9f1e-51669ff851d6" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/RevenuefromContractswithCustomerScheduleofRevenueDisaggregationbyLocationDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#RevenuefromContractswithCustomerScheduleofRevenueDisaggregationbyLocationDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/RevenuefromContractswithCustomerScheduleofRevenueDisaggregationbyLocationDetails" xlink:type="extended" id="ifd45b0a8bd5244e09c986c9ab0e66a4e_RevenuefromContractswithCustomerScheduleofRevenueDisaggregationbyLocationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_83875d1c-e049-4042-9275-8701008a05d6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_e3e90f20-3d74-4d01-9ac6-960aa88e9678" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_83875d1c-e049-4042-9275-8701008a05d6" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_e3e90f20-3d74-4d01-9ac6-960aa88e9678" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_82ea7a22-e3de-482c-8517-bde1757477b3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_83875d1c-e049-4042-9275-8701008a05d6" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_82ea7a22-e3de-482c-8517-bde1757477b3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_9da07112-fc08-4a92-b3b0-847ae4c2180e" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_82ea7a22-e3de-482c-8517-bde1757477b3" xlink:to="loc_srt_StatementGeographicalAxis_9da07112-fc08-4a92-b3b0-847ae4c2180e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_9da07112-fc08-4a92-b3b0-847ae4c2180e_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_9da07112-fc08-4a92-b3b0-847ae4c2180e" xlink:to="loc_srt_SegmentGeographicalDomain_9da07112-fc08-4a92-b3b0-847ae4c2180e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_61a15180-0771-4c8d-9f5f-3631f9264014" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_9da07112-fc08-4a92-b3b0-847ae4c2180e" xlink:to="loc_srt_SegmentGeographicalDomain_61a15180-0771-4c8d-9f5f-3631f9264014" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_UnitedStatesCanadaAndLatinAmericaMember_c72e8462-3f08-4e6d-8ad5-c8c9c3cf9f41" xlink:href="bsy-20210630.xsd#bsy_UnitedStatesCanadaAndLatinAmericaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_61a15180-0771-4c8d-9f5f-3631f9264014" xlink:to="loc_bsy_UnitedStatesCanadaAndLatinAmericaMember_c72e8462-3f08-4e6d-8ad5-c8c9c3cf9f41" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_923800e7-efdd-4066-a869-092aaaed8739" xlink:href="https://xbrl.sec.gov/country/2020/country-2020-01-31.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_UnitedStatesCanadaAndLatinAmericaMember_c72e8462-3f08-4e6d-8ad5-c8c9c3cf9f41" xlink:to="loc_country_US_923800e7-efdd-4066-a869-092aaaed8739" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EMEAMember_37bd5a41-bf84-4d82-beb4-2cc03f529ca2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EMEAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_61a15180-0771-4c8d-9f5f-3631f9264014" xlink:to="loc_us-gaap_EMEAMember_37bd5a41-bf84-4d82-beb4-2cc03f529ca2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_GB_ff27a9d9-3c98-410d-aa73-3f7eada37169" xlink:href="https://xbrl.sec.gov/country/2020/country-2020-01-31.xsd#country_GB"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EMEAMember_37bd5a41-bf84-4d82-beb4-2cc03f529ca2" xlink:to="loc_country_GB_ff27a9d9-3c98-410d-aa73-3f7eada37169" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AsiaPacificMember_1dda95d3-4d57-4ae0-863c-4ec3ba08e6f0" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_AsiaPacificMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_61a15180-0771-4c8d-9f5f-3631f9264014" xlink:to="loc_srt_AsiaPacificMember_1dda95d3-4d57-4ae0-863c-4ec3ba08e6f0" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/AcquisitionsNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#AcquisitionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/AcquisitionsNarrativeDetails" xlink:type="extended" id="i45d2ec4013bb4fdb8c20290687444427_AcquisitionsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_8c0eabf5-4635-42d9-bf69-550d2b5600d5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_79b39c8d-658f-4000-acd9-7d0999fac4d4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_8c0eabf5-4635-42d9-bf69-550d2b5600d5" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_79b39c8d-658f-4000-acd9-7d0999fac4d4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_a27ad36d-6716-4c66-a1dc-214b560efbd1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_8c0eabf5-4635-42d9-bf69-550d2b5600d5" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_a27ad36d-6716-4c66-a1dc-214b560efbd1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_d2021995-f8a9-40a8-b72b-141ad536f6f6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_8c0eabf5-4635-42d9-bf69-550d2b5600d5" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_d2021995-f8a9-40a8-b72b-141ad536f6f6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_b6e5cd67-8688-4e70-9c7d-ed220fe3bbdc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_8c0eabf5-4635-42d9-bf69-550d2b5600d5" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_b6e5cd67-8688-4e70-9c7d-ed220fe3bbdc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfBusinessesAcquired_29d78883-a9ea-4295-98f3-56af22e9afff" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NumberOfBusinessesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_8c0eabf5-4635-42d9-bf69-550d2b5600d5" xlink:to="loc_us-gaap_NumberOfBusinessesAcquired_29d78883-a9ea-4295-98f3-56af22e9afff" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsAdditionalDisclosuresAcquisitionCostExpensed_eda739c8-5b8d-4540-9b80-8c3c4f883403" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsAdditionalDisclosuresAcquisitionCostExpensed"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_8c0eabf5-4635-42d9-bf69-550d2b5600d5" xlink:to="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsAdditionalDisclosuresAcquisitionCostExpensed_eda739c8-5b8d-4540-9b80-8c3c4f883403" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_7d989318-dc70-4b9c-8a14-a9336f32c366" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_8c0eabf5-4635-42d9-bf69-550d2b5600d5" xlink:to="loc_us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_7d989318-dc70-4b9c-8a14-a9336f32c366" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_01cf6da6-f6c9-45a2-97fb-4b1a657d5483" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionsProFormaRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_8c0eabf5-4635-42d9-bf69-550d2b5600d5" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_01cf6da6-f6c9-45a2-97fb-4b1a657d5483" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_3acfc49e-ccf0-41a4-96dd-b1a72144a788" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_8c0eabf5-4635-42d9-bf69-550d2b5600d5" xlink:to="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_3acfc49e-ccf0-41a4-96dd-b1a72144a788" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_1a9a2966-9a8c-4f5f-a1fb-319b4f9233fe" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_3acfc49e-ccf0-41a4-96dd-b1a72144a788" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_1a9a2966-9a8c-4f5f-a1fb-319b4f9233fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_1a9a2966-9a8c-4f5f-a1fb-319b4f9233fe_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_1a9a2966-9a8c-4f5f-a1fb-319b4f9233fe" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_1a9a2966-9a8c-4f5f-a1fb-319b4f9233fe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_29e41ecd-8523-4862-98cb-9f0d4170ca47" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_1a9a2966-9a8c-4f5f-a1fb-319b4f9233fe" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_29e41ecd-8523-4862-98cb-9f0d4170ca47" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_8277f88e-a5fb-42dc-bdb3-73fbc2ad6ec2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_29e41ecd-8523-4862-98cb-9f0d4170ca47" xlink:to="loc_us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_8277f88e-a5fb-42dc-bdb3-73fbc2ad6ec2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_SeequentMember_e5e96b7f-b3df-4a58-81e7-471534d2b833" xlink:href="bsy-20210630.xsd#bsy_SeequentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_29e41ecd-8523-4862-98cb-9f0d4170ca47" xlink:to="loc_bsy_SeequentMember_e5e96b7f-b3df-4a58-81e7-471534d2b833" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrecurringAdjustmentAxis_4c15e88b-02fb-405f-ba5a-5d9724be5439" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NonrecurringAdjustmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_3acfc49e-ccf0-41a4-96dd-b1a72144a788" xlink:to="loc_us-gaap_NonrecurringAdjustmentAxis_4c15e88b-02fb-405f-ba5a-5d9724be5439" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrecurringAdjustmentDomain_4c15e88b-02fb-405f-ba5a-5d9724be5439_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NonrecurringAdjustmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_NonrecurringAdjustmentAxis_4c15e88b-02fb-405f-ba5a-5d9724be5439" xlink:to="loc_us-gaap_NonrecurringAdjustmentDomain_4c15e88b-02fb-405f-ba5a-5d9724be5439_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrecurringAdjustmentDomain_90a28ca8-9fe8-47b5-943a-5cdbd61c87f1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NonrecurringAdjustmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_NonrecurringAdjustmentAxis_4c15e88b-02fb-405f-ba5a-5d9724be5439" xlink:to="loc_us-gaap_NonrecurringAdjustmentDomain_90a28ca8-9fe8-47b5-943a-5cdbd61c87f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_AcquiredSupportContractsAdjustmentToRevenueMember_af015ec5-fda8-44da-a2c4-52160aa2f8f3" xlink:href="bsy-20210630.xsd#bsy_AcquiredSupportContractsAdjustmentToRevenueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonrecurringAdjustmentDomain_90a28ca8-9fe8-47b5-943a-5cdbd61c87f1" xlink:to="loc_bsy_AcquiredSupportContractsAdjustmentToRevenueMember_af015ec5-fda8-44da-a2c4-52160aa2f8f3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_1400d49d-2ab4-4d87-b64b-80a6bce33e5e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_3acfc49e-ccf0-41a4-96dd-b1a72144a788" xlink:to="loc_us-gaap_StatementClassOfStockAxis_1400d49d-2ab4-4d87-b64b-80a6bce33e5e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_1400d49d-2ab4-4d87-b64b-80a6bce33e5e_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_1400d49d-2ab4-4d87-b64b-80a6bce33e5e" xlink:to="loc_us-gaap_ClassOfStockDomain_1400d49d-2ab4-4d87-b64b-80a6bce33e5e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_e60355d4-1e28-4977-9c98-5bbaa7813f6f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_1400d49d-2ab4-4d87-b64b-80a6bce33e5e" xlink:to="loc_us-gaap_ClassOfStockDomain_e60355d4-1e28-4977-9c98-5bbaa7813f6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_1ff4a304-7f80-4561-8129-bca98ab038e3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_e60355d4-1e28-4977-9c98-5bbaa7813f6f" xlink:to="loc_us-gaap_CommonClassBMember_1ff4a304-7f80-4561-8129-bca98ab038e3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_35691c42-7042-42af-9a1e-44720af80c77" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_3acfc49e-ccf0-41a4-96dd-b1a72144a788" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_35691c42-7042-42af-9a1e-44720af80c77" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_35691c42-7042-42af-9a1e-44720af80c77_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_35691c42-7042-42af-9a1e-44720af80c77" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_35691c42-7042-42af-9a1e-44720af80c77_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_7cf553d4-4c84-42d7-b854-e0178c150425" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_35691c42-7042-42af-9a1e-44720af80c77" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_7cf553d4-4c84-42d7-b854-e0178c150425" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_fd44e362-e998-4c31-9e7a-20c976652c31" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_7cf553d4-4c84-42d7-b854-e0178c150425" xlink:to="loc_us-gaap_SubsequentEventMember_fd44e362-e998-4c31-9e7a-20c976652c31" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/AcquisitionsScheduleofCashPaidandAcquiredforAcquisitionsDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#AcquisitionsScheduleofCashPaidandAcquiredforAcquisitionsDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/AcquisitionsScheduleofCashPaidandAcquiredforAcquisitionsDetails" xlink:type="extended" id="i5044ef6fb96042169d576672dc05925d_AcquisitionsScheduleofCashPaidandAcquiredforAcquisitionsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_95ba8b6d-3d97-4a13-8546-9e567628d6ae" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfBusinessesAcquired_f1f41f3e-3eea-4c93-90d6-b50404c5b926" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NumberOfBusinessesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_95ba8b6d-3d97-4a13-8546-9e567628d6ae" xlink:to="loc_us-gaap_NumberOfBusinessesAcquired_f1f41f3e-3eea-4c93-90d6-b50404c5b926" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_477d279b-fe73-475b-a2e0-eefed3e2f27b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_95ba8b6d-3d97-4a13-8546-9e567628d6ae" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_477d279b-fe73-475b-a2e0-eefed3e2f27b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAcquiredFromAcquisition_0a6c6125-4bd0-4c6d-9702-818325de4a22" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashAcquiredFromAcquisition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_95ba8b6d-3d97-4a13-8546-9e567628d6ae" xlink:to="loc_us-gaap_CashAcquiredFromAcquisition_0a6c6125-4bd0-4c6d-9702-818325de4a22" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_6c5fca2d-295a-413d-9b6e-16f708ba0037" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_95ba8b6d-3d97-4a13-8546-9e567628d6ae" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_6c5fca2d-295a-413d-9b6e-16f708ba0037" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EscrowDeposit_107046ff-9f15-4426-be12-bd8e80e821c7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EscrowDeposit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_95ba8b6d-3d97-4a13-8546-9e567628d6ae" xlink:to="loc_us-gaap_EscrowDeposit_107046ff-9f15-4426-be12-bd8e80e821c7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_d0565dab-1bf1-4c8c-bbc3-1c50cee8d286" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_95ba8b6d-3d97-4a13-8546-9e567628d6ae" xlink:to="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_d0565dab-1bf1-4c8c-bbc3-1c50cee8d286" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_787e8411-a501-4679-9f0f-b8a31cdee602" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_d0565dab-1bf1-4c8c-bbc3-1c50cee8d286" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_787e8411-a501-4679-9f0f-b8a31cdee602" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_787e8411-a501-4679-9f0f-b8a31cdee602_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_787e8411-a501-4679-9f0f-b8a31cdee602" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_787e8411-a501-4679-9f0f-b8a31cdee602_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0ca4c1e9-0870-46b6-9b33-16f8c1ba1eca" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_787e8411-a501-4679-9f0f-b8a31cdee602" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0ca4c1e9-0870-46b6-9b33-16f8c1ba1eca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_a125aeb4-1c60-4606-af82-7139aa001609" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0ca4c1e9-0870-46b6-9b33-16f8c1ba1eca" xlink:to="loc_us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_a125aeb4-1c60-4606-af82-7139aa001609" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/AcquisitionsScheduleofContingentandNonContingentConsiderationFairValueDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#AcquisitionsScheduleofContingentandNonContingentConsiderationFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/AcquisitionsScheduleofContingentandNonContingentConsiderationFairValueDetails" xlink:type="extended" id="i3e3ead67f0f94b2f9994768975da093d_AcquisitionsScheduleofContingentandNonContingentConsiderationFairValueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_dd0c9177-3f03-4bb6-b1cb-532dbf0919fc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionContingentConsiderationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent_e4f39f52-0796-4371-839f-c33c075f0cf5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_dd0c9177-3f03-4bb6-b1cb-532dbf0919fc" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent_e4f39f52-0796-4371-839f-c33c075f0cf5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent_0d68435a-49a0-438e-b90a-8ce557065f1f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_dd0c9177-3f03-4bb6-b1cb-532dbf0919fc" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent_0d68435a-49a0-438e-b90a-8ce557065f1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_bc2164b4-b27f-4325-9e2c-6ad0e7aebb98" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_dd0c9177-3f03-4bb6-b1cb-532dbf0919fc" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_bc2164b4-b27f-4325-9e2c-6ad0e7aebb98" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_BusinessCombinationConsiderationPayableCurrent_e71b65dc-355b-4a4e-b2be-4f3000b8fd2e" xlink:href="bsy-20210630.xsd#bsy_BusinessCombinationConsiderationPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_dd0c9177-3f03-4bb6-b1cb-532dbf0919fc" xlink:to="loc_bsy_BusinessCombinationConsiderationPayableCurrent_e71b65dc-355b-4a4e-b2be-4f3000b8fd2e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_BusinessCombinationConsiderationPayableNoncurrent_35aefaef-61df-42e2-9ef3-ddc71645d0ab" xlink:href="bsy-20210630.xsd#bsy_BusinessCombinationConsiderationPayableNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_dd0c9177-3f03-4bb6-b1cb-532dbf0919fc" xlink:to="loc_bsy_BusinessCombinationConsiderationPayableNoncurrent_35aefaef-61df-42e2-9ef3-ddc71645d0ab" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_BusinessCombinationConsiderationPayable_5d8fb3b6-5a75-4907-9d60-e0e994b4a39a" xlink:href="bsy-20210630.xsd#bsy_BusinessCombinationConsiderationPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_dd0c9177-3f03-4bb6-b1cb-532dbf0919fc" xlink:to="loc_bsy_BusinessCombinationConsiderationPayable_5d8fb3b6-5a75-4907-9d60-e0e994b4a39a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionContingentConsiderationTable_4dd0e399-6354-4d97-b714-7a75f3821986" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionContingentConsiderationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionContingentConsiderationLineItems_dd0c9177-3f03-4bb6-b1cb-532dbf0919fc" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionContingentConsiderationTable_4dd0e399-6354-4d97-b714-7a75f3821986" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_404b486a-867b-4284-b285-59aec8a1a468" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionContingentConsiderationTable_4dd0e399-6354-4d97-b714-7a75f3821986" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_404b486a-867b-4284-b285-59aec8a1a468" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_404b486a-867b-4284-b285-59aec8a1a468_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_404b486a-867b-4284-b285-59aec8a1a468" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_404b486a-867b-4284-b285-59aec8a1a468_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_cea9bbde-bd70-4049-85a1-e629adb5dc48" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_404b486a-867b-4284-b285-59aec8a1a468" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_cea9bbde-bd70-4049-85a1-e629adb5dc48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_9786c5e2-921e-4ef0-9ed3-ef1d68ce6146" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_cea9bbde-bd70-4049-85a1-e629adb5dc48" xlink:to="loc_us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_9786c5e2-921e-4ef0-9ed3-ef1d68ce6146" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/AcquisitionsScheduleofConsiderationandNetAssetsAcquiredDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#AcquisitionsScheduleofConsiderationandNetAssetsAcquiredDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/AcquisitionsScheduleofConsiderationandNetAssetsAcquiredDetails" xlink:type="extended" id="if7876fd80128447da83198444c6aad3b_AcquisitionsScheduleofConsiderationandNetAssetsAcquiredDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_9b5a333f-91f5-4c99-ab4c-743543b8b181" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_7ff7c7fb-35ab-45dd-bf50-d33785651ab6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_9b5a333f-91f5-4c99-ab4c-743543b8b181" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_7ff7c7fb-35ab-45dd-bf50-d33785651ab6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_b6407949-22d5-4d9e-8f26-5f3d87d04337" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_9b5a333f-91f5-4c99-ab4c-743543b8b181" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_b6407949-22d5-4d9e-8f26-5f3d87d04337" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_bfb0b575-8ad0-43b1-a561-3182c5dae2e3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_9b5a333f-91f5-4c99-ab4c-743543b8b181" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_bfb0b575-8ad0-43b1-a561-3182c5dae2e3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_BusinessCombinationContingentConsiderationLiabilityInitialValue_540170b1-1aae-4582-af03-53677ea05674" xlink:href="bsy-20210630.xsd#bsy_BusinessCombinationContingentConsiderationLiabilityInitialValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_9b5a333f-91f5-4c99-ab4c-743543b8b181" xlink:to="loc_bsy_BusinessCombinationContingentConsiderationLiabilityInitialValue_540170b1-1aae-4582-af03-53677ea05674" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_BusinessCombinationConsiderationPayableInitialValue_2f927400-0228-4d12-a757-f1780d367be4" xlink:href="bsy-20210630.xsd#bsy_BusinessCombinationConsiderationPayableInitialValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_9b5a333f-91f5-4c99-ab4c-743543b8b181" xlink:to="loc_bsy_BusinessCombinationConsiderationPayableInitialValue_2f927400-0228-4d12-a757-f1780d367be4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_b945da3c-7f8e-4a0d-91db-2fbad239b054" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_9b5a333f-91f5-4c99-ab4c-743543b8b181" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_b945da3c-7f8e-4a0d-91db-2fbad239b054" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_9b5a333f-91f5-4c99-ab4c-743543b8b181" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_23f93358-10ff-4a50-b6b4-a436446bb459" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_23f93358-10ff-4a50-b6b4-a436446bb459" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_a53545f9-58df-4000-8266-db07492e933b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_a53545f9-58df-4000-8266-db07492e933b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentAssetsOperatingLeaseRightOfUseAsset_dfeebef8-df96-466d-921b-0c40d20bc2a1" xlink:href="bsy-20210630.xsd#bsy_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentAssetsOperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:to="loc_bsy_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentAssetsOperatingLeaseRightOfUseAsset_dfeebef8-df96-466d-921b-0c40d20bc2a1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_d7b5affc-6551-4e0a-beac-5d1b00307706" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_d7b5affc-6551-4e0a-beac-5d1b00307706" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities_f51fbdd1-1097-4fee-8880-9b47268083e7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities_f51fbdd1-1097-4fee-8880-9b47268083e7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_c8b75c6c-76a8-4168-bae6-4b663c35b523" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_c8b75c6c-76a8-4168-bae6-4b663c35b523" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_c9856e39-697f-456b-84e6-16021cd7969a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_c9856e39-697f-456b-84e6-16021cd7969a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets_4f42b728-9c82-42ef-a6f8-49eb4f3f378f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets_4f42b728-9c82-42ef-a6f8-49eb4f3f378f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther_3492e5ea-ea1d-4d25-bc00-4806b965a982" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther_3492e5ea-ea1d-4d25-bc00-4806b965a982" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue_b912cd40-55f4-4985-93c3-2aadeb2dca5b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesDeferredRevenue_b912cd40-55f4-4985-93c3-2aadeb2dca5b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOperatingLeaseLiabilityNoncurrent_d7817e46-020a-4f7a-ae63-550379c9e368" xlink:href="bsy-20210630.xsd#bsy_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:to="loc_bsy_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOperatingLeaseLiabilityNoncurrent_d7817e46-020a-4f7a-ae63-550379c9e368" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_b49a9c65-ba95-41db-8029-304e9d725681" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_b49a9c65-ba95-41db-8029-304e9d725681" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_d2ac854c-6b26-4bab-92e0-89a82261a1a6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_d2ac854c-6b26-4bab-92e0-89a82261a1a6" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_acbebbbd-47a0-43f6-910b-4d779d86dbfe" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_acbebbbd-47a0-43f6-910b-4d779d86dbfe" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_1ab8244f-f05d-40a9-847a-7844507b30db" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_1ab8244f-f05d-40a9-847a-7844507b30db" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_2ae82382-9274-483d-923a-3f7b651c3f00" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:to="loc_us-gaap_Goodwill_2ae82382-9274-483d-923a-3f7b651c3f00" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_51478f52-f418-449a-a6cc-63055c18bdb5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNetAbstract_924ab91e-c40f-4e9c-afdc-ac9b604f27e9" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_51478f52-f418-449a-a6cc-63055c18bdb5" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_998355f7-911b-4b41-a774-49c831783922" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_9b5a333f-91f5-4c99-ab4c-743543b8b181" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_998355f7-911b-4b41-a774-49c831783922" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_SaleOfStockNumberOfSharesIssuedInTransactionSubjectToEmploymentServiceConditions_020be688-8900-4d21-8415-950e1b859f5b" xlink:href="bsy-20210630.xsd#bsy_SaleOfStockNumberOfSharesIssuedInTransactionSubjectToEmploymentServiceConditions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_9b5a333f-91f5-4c99-ab4c-743543b8b181" xlink:to="loc_bsy_SaleOfStockNumberOfSharesIssuedInTransactionSubjectToEmploymentServiceConditions_020be688-8900-4d21-8415-950e1b859f5b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_fa3d8e85-5b18-4d2f-8a01-b30af318c0ef" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_9b5a333f-91f5-4c99-ab4c-743543b8b181" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_fa3d8e85-5b18-4d2f-8a01-b30af318c0ef" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_ac1181f7-e52d-4335-a066-81e28f1868a9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_9b5a333f-91f5-4c99-ab4c-743543b8b181" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_ac1181f7-e52d-4335-a066-81e28f1868a9" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentEquityInterests_36c38c01-8b1b-4a19-9532-74d0e38a7551" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentEquityInterests"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_9b5a333f-91f5-4c99-ab4c-743543b8b181" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentEquityInterests_36c38c01-8b1b-4a19-9532-74d0e38a7551" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_22b7652d-d371-4071-8a6b-2ba5df7bb49a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLineItems_9b5a333f-91f5-4c99-ab4c-743543b8b181" xlink:to="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_22b7652d-d371-4071-8a6b-2ba5df7bb49a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_fe9d511d-3302-41a2-86ef-7d92ee1fec10" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_22b7652d-d371-4071-8a6b-2ba5df7bb49a" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_fe9d511d-3302-41a2-86ef-7d92ee1fec10" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_fe9d511d-3302-41a2-86ef-7d92ee1fec10_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_fe9d511d-3302-41a2-86ef-7d92ee1fec10" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_fe9d511d-3302-41a2-86ef-7d92ee1fec10_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8d99069f-1456-4c5c-89b8-ba4b3595e3f4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_fe9d511d-3302-41a2-86ef-7d92ee1fec10" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8d99069f-1456-4c5c-89b8-ba4b3595e3f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_0ab0bf63-7a7c-47b5-8053-dc349d536645" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8d99069f-1456-4c5c-89b8-ba4b3595e3f4" xlink:to="loc_us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_0ab0bf63-7a7c-47b5-8053-dc349d536645" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_SeequentMember_9ec9c403-9e97-4da9-9cd6-d8bec235e54b" xlink:href="bsy-20210630.xsd#bsy_SeequentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8d99069f-1456-4c5c-89b8-ba4b3595e3f4" xlink:to="loc_bsy_SeequentMember_9ec9c403-9e97-4da9-9cd6-d8bec235e54b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_49caee66-1014-4943-b2d6-c1652518149a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_22b7652d-d371-4071-8a6b-2ba5df7bb49a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_49caee66-1014-4943-b2d6-c1652518149a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_49caee66-1014-4943-b2d6-c1652518149a_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_49caee66-1014-4943-b2d6-c1652518149a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_49caee66-1014-4943-b2d6-c1652518149a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_9a33dbb2-0b29-46a7-9911-a57a0ac30093" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_49caee66-1014-4943-b2d6-c1652518149a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_9a33dbb2-0b29-46a7-9911-a57a0ac30093" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerSoftwareIntangibleAssetMember_a9498f81-126e-4732-8fee-00dfcf998f2c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ComputerSoftwareIntangibleAssetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_9a33dbb2-0b29-46a7-9911-a57a0ac30093" xlink:to="loc_us-gaap_ComputerSoftwareIntangibleAssetMember_a9498f81-126e-4732-8fee-00dfcf998f2c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_fed87262-42d7-41a9-a03d-ae903b25b884" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_9a33dbb2-0b29-46a7-9911-a57a0ac30093" xlink:to="loc_us-gaap_CustomerRelationshipsMember_fed87262-42d7-41a9-a03d-ae903b25b884" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksMember_536365a1-ce33-484d-8ede-3fa0858d9124" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TrademarksMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_9a33dbb2-0b29-46a7-9911-a57a0ac30093" xlink:to="loc_us-gaap_TrademarksMember_536365a1-ce33-484d-8ede-3fa0858d9124" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncompeteAgreementsMember_2bfda140-48c3-46bc-bd2a-12a3aeb0b210" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NoncompeteAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_9a33dbb2-0b29-46a7-9911-a57a0ac30093" xlink:to="loc_us-gaap_NoncompeteAgreementsMember_2bfda140-48c3-46bc-bd2a-12a3aeb0b210" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InProcessResearchAndDevelopmentMember_20c9f317-b85f-42d8-bb60-3c9cb2cbde37" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InProcessResearchAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_9a33dbb2-0b29-46a7-9911-a57a0ac30093" xlink:to="loc_us-gaap_InProcessResearchAndDevelopmentMember_20c9f317-b85f-42d8-bb60-3c9cb2cbde37" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_72197146-b90b-417f-a3e9-dd5d77a4e1cf" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_22b7652d-d371-4071-8a6b-2ba5df7bb49a" xlink:to="loc_srt_RangeAxis_72197146-b90b-417f-a3e9-dd5d77a4e1cf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_72197146-b90b-417f-a3e9-dd5d77a4e1cf_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_72197146-b90b-417f-a3e9-dd5d77a4e1cf" xlink:to="loc_srt_RangeMember_72197146-b90b-417f-a3e9-dd5d77a4e1cf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_226cb571-5985-40af-9fab-3fb8141d0ace" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_72197146-b90b-417f-a3e9-dd5d77a4e1cf" xlink:to="loc_srt_RangeMember_226cb571-5985-40af-9fab-3fb8141d0ace" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_WeightedAverageMember_fa28d9e3-59d7-445e-8c26-0da26d304aa8" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_WeightedAverageMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_226cb571-5985-40af-9fab-3fb8141d0ace" xlink:to="loc_srt_WeightedAverageMember_fa28d9e3-59d7-445e-8c26-0da26d304aa8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_ae6e0921-7332-46df-8a9f-b5a9ad41c915" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_22b7652d-d371-4071-8a6b-2ba5df7bb49a" xlink:to="loc_us-gaap_StatementClassOfStockAxis_ae6e0921-7332-46df-8a9f-b5a9ad41c915" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_ae6e0921-7332-46df-8a9f-b5a9ad41c915_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_ae6e0921-7332-46df-8a9f-b5a9ad41c915" xlink:to="loc_us-gaap_ClassOfStockDomain_ae6e0921-7332-46df-8a9f-b5a9ad41c915_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_0913c2c3-a6ca-4793-bb87-548f1b2a5df6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_ae6e0921-7332-46df-8a9f-b5a9ad41c915" xlink:to="loc_us-gaap_ClassOfStockDomain_0913c2c3-a6ca-4793-bb87-548f1b2a5df6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_dc6ef151-5176-4f62-943b-38764af9a543" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_0913c2c3-a6ca-4793-bb87-548f1b2a5df6" xlink:to="loc_us-gaap_CommonClassBMember_dc6ef151-5176-4f62-943b-38764af9a543" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_b93dd64b-7a50-444a-aeb7-f79580956f5c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsTable_22b7652d-d371-4071-8a6b-2ba5df7bb49a" xlink:to="loc_us-gaap_AwardTypeAxis_b93dd64b-7a50-444a-aeb7-f79580956f5c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b93dd64b-7a50-444a-aeb7-f79580956f5c_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_b93dd64b-7a50-444a-aeb7-f79580956f5c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b93dd64b-7a50-444a-aeb7-f79580956f5c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_946107fc-b3e0-49c4-8f28-57c159976f7e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_b93dd64b-7a50-444a-aeb7-f79580956f5c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_946107fc-b3e0-49c4-8f28-57c159976f7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_CommonClassBStockSubjectToServiceConditionsMember_ae50ded1-d55b-4156-b3fa-e91bd728dcf1" xlink:href="bsy-20210630.xsd#bsy_CommonClassBStockSubjectToServiceConditionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_946107fc-b3e0-49c4-8f28-57c159976f7e" xlink:to="loc_bsy_CommonClassBStockSubjectToServiceConditionsMember_ae50ded1-d55b-4156-b3fa-e91bd728dcf1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/PropertyandEquipmentNetScheduleofPropertyandEquipmentNetDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#PropertyandEquipmentNetScheduleofPropertyandEquipmentNetDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/PropertyandEquipmentNetScheduleofPropertyandEquipmentNetDetails" xlink:type="extended" id="i5cb4816122c1455eb3b4afb6e7a4592b_PropertyandEquipmentNetScheduleofPropertyandEquipmentNetDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_68688f0a-ecac-4c0d-9ca7-85c804fbac8b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization_70a1fa33-2dba-4595-bd75-f3d4ea8004b0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_68688f0a-ecac-4c0d-9ca7-85c804fbac8b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization_70a1fa33-2dba-4595-bd75-f3d4ea8004b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_698fb03a-3ee9-4a65-bc57-8032bcec7f87" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_68688f0a-ecac-4c0d-9ca7-85c804fbac8b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_698fb03a-3ee9-4a65-bc57-8032bcec7f87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_d741783f-a8ca-492a-90ba-fd4697242f51" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_68688f0a-ecac-4c0d-9ca7-85c804fbac8b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_d741783f-a8ca-492a-90ba-fd4697242f51" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_1b171abc-1a93-4263-9d78-767a4e9a4c66" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_68688f0a-ecac-4c0d-9ca7-85c804fbac8b" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_1b171abc-1a93-4263-9d78-767a4e9a4c66" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_45a89a0a-58e5-426b-9532-11fe027dbfcd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_1b171abc-1a93-4263-9d78-767a4e9a4c66" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_45a89a0a-58e5-426b-9532-11fe027dbfcd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_45a89a0a-58e5-426b-9532-11fe027dbfcd_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_45a89a0a-58e5-426b-9532-11fe027dbfcd" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_45a89a0a-58e5-426b-9532-11fe027dbfcd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1055981d-9c97-49bf-89e1-b398d13fa275" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_45a89a0a-58e5-426b-9532-11fe027dbfcd" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1055981d-9c97-49bf-89e1-b398d13fa275" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandMember_c8192950-5f49-4555-bc8c-9b7321f3517d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1055981d-9c97-49bf-89e1-b398d13fa275" xlink:to="loc_us-gaap_LandMember_c8192950-5f49-4555-bc8c-9b7321f3517d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BuildingAndBuildingImprovementsMember_b1cad2fa-3744-4cb3-9fbf-6d3d06e9ee10" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BuildingAndBuildingImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1055981d-9c97-49bf-89e1-b398d13fa275" xlink:to="loc_us-gaap_BuildingAndBuildingImprovementsMember_b1cad2fa-3744-4cb3-9fbf-6d3d06e9ee10" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_ComputerEquipmentAndSoftwareMember_015b8857-6572-49a3-8e97-57c0f8d19e2c" xlink:href="bsy-20210630.xsd#bsy_ComputerEquipmentAndSoftwareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1055981d-9c97-49bf-89e1-b398d13fa275" xlink:to="loc_bsy_ComputerEquipmentAndSoftwareMember_015b8857-6572-49a3-8e97-57c0f8d19e2c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_ea753cb3-1fc5-4b12-ad78-77ef88f04867" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1055981d-9c97-49bf-89e1-b398d13fa275" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_ea753cb3-1fc5-4b12-ad78-77ef88f04867" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AirTransportationEquipmentMember_c76685f3-c8b7-4266-943a-48884704fa58" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AirTransportationEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1055981d-9c97-49bf-89e1-b398d13fa275" xlink:to="loc_us-gaap_AirTransportationEquipmentMember_c76685f3-c8b7-4266-943a-48884704fa58" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCapitalizedPropertyPlantAndEquipmentMember_56350c79-bf1d-4a3c-8245-7764ca12104c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherCapitalizedPropertyPlantAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_1055981d-9c97-49bf-89e1-b398d13fa275" xlink:to="loc_us-gaap_OtherCapitalizedPropertyPlantAndEquipmentMember_56350c79-bf1d-4a3c-8245-7764ca12104c" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/GoodwillandOtherIntangibleAssetsIntangibleAssetsOtherthanGoodwillDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#GoodwillandOtherIntangibleAssetsIntangibleAssetsOtherthanGoodwillDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/GoodwillandOtherIntangibleAssetsIntangibleAssetsOtherthanGoodwillDetails" xlink:type="extended" id="i3ef6760db3eb405c89393c4fdf9fe187_GoodwillandOtherIntangibleAssetsIntangibleAssetsOtherthanGoodwillDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_215215d1-3cbf-442a-89f2-c73dfd5f63dc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_5a15211b-fb11-4cf4-8d77-d13748429d2a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_215215d1-3cbf-442a-89f2-c73dfd5f63dc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_5a15211b-fb11-4cf4-8d77-d13748429d2a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_06682169-ba24-453c-bd4f-e4bccd326cab" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_5a15211b-fb11-4cf4-8d77-d13748429d2a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_06682169-ba24-453c-bd4f-e4bccd326cab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_9a69a638-008e-42c7-8400-631e103c381a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_5a15211b-fb11-4cf4-8d77-d13748429d2a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_9a69a638-008e-42c7-8400-631e103c381a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_35a41a4e-02f5-4c34-9b35-32ad2e545f76" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_5a15211b-fb11-4cf4-8d77-d13748429d2a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_35a41a4e-02f5-4c34-9b35-32ad2e545f76" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_c4d6321b-221b-4631-8a1c-bb93782326af" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_5a15211b-fb11-4cf4-8d77-d13748429d2a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_c4d6321b-221b-4631-8a1c-bb93782326af" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillAbstract_ad7d3d5f-31fc-43ee-8668-81bb9cdb4b15" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_215215d1-3cbf-442a-89f2-c73dfd5f63dc" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillAbstract_ad7d3d5f-31fc-43ee-8668-81bb9cdb4b15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_7f0a5704-547e-4181-b37d-cd0c22c091fb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillAbstract_ad7d3d5f-31fc-43ee-8668-81bb9cdb4b15" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_7f0a5704-547e-4181-b37d-cd0c22c091fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_b31032ca-842d-4fac-b288-82fbfe160272" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_215215d1-3cbf-442a-89f2-c73dfd5f63dc" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_b31032ca-842d-4fac-b288-82fbfe160272" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_f9d5fdd5-8f41-4ab6-8c2b-e9c1244f6be2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_215215d1-3cbf-442a-89f2-c73dfd5f63dc" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_f9d5fdd5-8f41-4ab6-8c2b-e9c1244f6be2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_e5db1d4c-f4e5-4e07-9e38-02c9e5594eda" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_215215d1-3cbf-442a-89f2-c73dfd5f63dc" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_e5db1d4c-f4e5-4e07-9e38-02c9e5594eda" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_77fb8796-ef9e-48f4-b44f-7b7fcf7bb0e1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_e5db1d4c-f4e5-4e07-9e38-02c9e5594eda" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_77fb8796-ef9e-48f4-b44f-7b7fcf7bb0e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_77fb8796-ef9e-48f4-b44f-7b7fcf7bb0e1_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_77fb8796-ef9e-48f4-b44f-7b7fcf7bb0e1" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_77fb8796-ef9e-48f4-b44f-7b7fcf7bb0e1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_39c7a1ec-a950-4418-962b-cccb8aa98c89" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_77fb8796-ef9e-48f4-b44f-7b7fcf7bb0e1" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_39c7a1ec-a950-4418-962b-cccb8aa98c89" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerSoftwareIntangibleAssetMember_bc4027cc-1eca-4ad6-833a-5e1bf8ed1d3d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ComputerSoftwareIntangibleAssetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_39c7a1ec-a950-4418-962b-cccb8aa98c89" xlink:to="loc_us-gaap_ComputerSoftwareIntangibleAssetMember_bc4027cc-1eca-4ad6-833a-5e1bf8ed1d3d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_829473de-95d5-4c42-b32f-e322d4ed1fe7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_39c7a1ec-a950-4418-962b-cccb8aa98c89" xlink:to="loc_us-gaap_CustomerRelationshipsMember_829473de-95d5-4c42-b32f-e322d4ed1fe7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksMember_e56c6665-a94a-46aa-8d16-1c66281515d0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TrademarksMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_39c7a1ec-a950-4418-962b-cccb8aa98c89" xlink:to="loc_us-gaap_TrademarksMember_e56c6665-a94a-46aa-8d16-1c66281515d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncompeteAgreementsMember_a953756b-7600-48cd-9acc-8d0c4f408ad1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NoncompeteAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_39c7a1ec-a950-4418-962b-cccb8aa98c89" xlink:to="loc_us-gaap_NoncompeteAgreementsMember_a953756b-7600-48cd-9acc-8d0c4f408ad1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_50d36454-ec04-48b0-a33f-d9da96b35538" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_e5db1d4c-f4e5-4e07-9e38-02c9e5594eda" xlink:to="loc_srt_RangeAxis_50d36454-ec04-48b0-a33f-d9da96b35538" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_50d36454-ec04-48b0-a33f-d9da96b35538_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_50d36454-ec04-48b0-a33f-d9da96b35538" xlink:to="loc_srt_RangeMember_50d36454-ec04-48b0-a33f-d9da96b35538_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_8aa688e8-40dc-48dc-91f6-1d8fc16c29af" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_50d36454-ec04-48b0-a33f-d9da96b35538" xlink:to="loc_srt_RangeMember_8aa688e8-40dc-48dc-91f6-1d8fc16c29af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_6e409023-c08c-47ba-92ec-4574a4bc544f" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_8aa688e8-40dc-48dc-91f6-1d8fc16c29af" xlink:to="loc_srt_MinimumMember_6e409023-c08c-47ba-92ec-4574a4bc544f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_3a6278e7-cbbb-4cd1-899e-edbdd8057548" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_8aa688e8-40dc-48dc-91f6-1d8fc16c29af" xlink:to="loc_srt_MaximumMember_3a6278e7-cbbb-4cd1-899e-edbdd8057548" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_828650c5-dfb8-4639-a5d2-4cb23567ff80" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_e5db1d4c-f4e5-4e07-9e38-02c9e5594eda" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_828650c5-dfb8-4639-a5d2-4cb23567ff80" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_828650c5-dfb8-4639-a5d2-4cb23567ff80_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_828650c5-dfb8-4639-a5d2-4cb23567ff80" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_828650c5-dfb8-4639-a5d2-4cb23567ff80_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_2f021f91-8016-47c2-8e4b-c0c93af5b02f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_828650c5-dfb8-4639-a5d2-4cb23567ff80" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_2f021f91-8016-47c2-8e4b-c0c93af5b02f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InProcessResearchAndDevelopmentMember_a7e8f610-3de3-4e0c-970a-8c332930a54d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InProcessResearchAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_2f021f91-8016-47c2-8e4b-c0c93af5b02f" xlink:to="loc_us-gaap_InProcessResearchAndDevelopmentMember_a7e8f610-3de3-4e0c-970a-8c332930a54d" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/InvestmentsDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#InvestmentsDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/InvestmentsDetails" xlink:type="extended" id="i57cb7d7d21f848f280f415ab560de6ef_InvestmentsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_f8758e8c-aa75-4907-b861-2d35474f2e4f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_e93ccdcf-2af6-4ed6-8e97-f10e58d631bd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_f8758e8c-aa75-4907-b861-2d35474f2e4f" xlink:to="loc_us-gaap_EquityMethodInvestments_e93ccdcf-2af6-4ed6-8e97-f10e58d631bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount_365490df-35e1-4c2b-9c30-3b467b23fc35" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_f8758e8c-aa75-4907-b861-2d35474f2e4f" xlink:to="loc_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount_365490df-35e1-4c2b-9c30-3b467b23fc35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_f4c5a438-1669-4a77-b132-aa5f99cd6385" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_f8758e8c-aa75-4907-b861-2d35474f2e4f" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_f4c5a438-1669-4a77-b132-aa5f99cd6385" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireEquityMethodInvestments_af88b45e-062b-4294-b38d-2466bcd45a99" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquireEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_f8758e8c-aa75-4907-b861-2d35474f2e4f" xlink:to="loc_us-gaap_PaymentsToAcquireEquityMethodInvestments_af88b45e-062b-4294-b38d-2466bcd45a99" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment_ae05fa83-a475-4635-9058-1dc9b4cdb6a1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_f8758e8c-aa75-4907-b861-2d35474f2e4f" xlink:to="loc_us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment_ae05fa83-a475-4635-9058-1dc9b4cdb6a1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_3675f622-248c-4420-abb4-46cca7157c97" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_f8758e8c-aa75-4907-b861-2d35474f2e4f" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_3675f622-248c-4420-abb4-46cca7157c97" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_32ced36d-b16f-4ac0-a9b9-b333730e6e0c" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_3675f622-248c-4420-abb4-46cca7157c97" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_32ced36d-b16f-4ac0-a9b9-b333730e6e0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_32ced36d-b16f-4ac0-a9b9-b333730e6e0c_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_32ced36d-b16f-4ac0-a9b9-b333730e6e0c" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_32ced36d-b16f-4ac0-a9b9-b333730e6e0c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_c98b4fc7-7d93-489a-9651-4caaebb0bcce" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_32ced36d-b16f-4ac0-a9b9-b333730e6e0c" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_c98b4fc7-7d93-489a-9651-4caaebb0bcce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DigitalConstructionWorksIncMember_221b1841-9de0-4316-ae3e-7f83c057a5c6" xlink:href="bsy-20210630.xsd#bsy_DigitalConstructionWorksIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_c98b4fc7-7d93-489a-9651-4caaebb0bcce" xlink:to="loc_bsy_DigitalConstructionWorksIncMember_221b1841-9de0-4316-ae3e-7f83c057a5c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_SeequentMember_456737d9-8d39-427f-bde2-e3afb6a34c9b" xlink:href="bsy-20210630.xsd#bsy_SeequentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_c98b4fc7-7d93-489a-9651-4caaebb0bcce" xlink:to="loc_bsy_SeequentMember_456737d9-8d39-427f-bde2-e3afb6a34c9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_0af1265a-2977-41f6-88ce-bbb5df7c68eb" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_3675f622-248c-4420-abb4-46cca7157c97" xlink:to="loc_dei_LegalEntityAxis_0af1265a-2977-41f6-88ce-bbb5df7c68eb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_0af1265a-2977-41f6-88ce-bbb5df7c68eb_default" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_0af1265a-2977-41f6-88ce-bbb5df7c68eb" xlink:to="loc_dei_EntityDomain_0af1265a-2977-41f6-88ce-bbb5df7c68eb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01304754-fda4-4f79-9b16-38ee666a3d6f" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_0af1265a-2977-41f6-88ce-bbb5df7c68eb" xlink:to="loc_dei_EntityDomain_01304754-fda4-4f79-9b16-38ee666a3d6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TopconMember_96f55ea9-850e-4081-8403-13579e163986" xlink:href="bsy-20210630.xsd#bsy_TopconMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01304754-fda4-4f79-9b16-38ee666a3d6f" xlink:to="loc_bsy_TopconMember_96f55ea9-850e-4081-8403-13579e163986" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_072e0824-1fc1-41d6-9f17-2748be96fbda" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_3675f622-248c-4420-abb4-46cca7157c97" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_072e0824-1fc1-41d6-9f17-2748be96fbda" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_072e0824-1fc1-41d6-9f17-2748be96fbda_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_072e0824-1fc1-41d6-9f17-2748be96fbda" xlink:to="loc_us-gaap_RelatedPartyDomain_072e0824-1fc1-41d6-9f17-2748be96fbda_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_f6b4d2f7-b48e-4bcd-940c-f95b4e15159d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_072e0824-1fc1-41d6-9f17-2748be96fbda" xlink:to="loc_us-gaap_RelatedPartyDomain_f6b4d2f7-b48e-4bcd-940c-f95b4e15159d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvesteeMember_edab4721-58e0-44bf-9f55-92973625f557" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityMethodInvesteeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_f6b4d2f7-b48e-4bcd-940c-f95b4e15159d" xlink:to="loc_us-gaap_EquityMethodInvesteeMember_edab4721-58e0-44bf-9f55-92973625f557" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/LeasesNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#LeasesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/LeasesNarrativeDetails" xlink:type="extended" id="ibe9e494971874238950bb99de8aa8a72_LeasesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_3cd107b4-392c-4fe2-aef9-a45943ae6619" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_e4e38982-e4a8-4de2-9199-2812de9dd140" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LesseeOperatingLeaseRemainingLeaseTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3cd107b4-392c-4fe2-aef9-a45943ae6619" xlink:to="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_e4e38982-e4a8-4de2-9199-2812de9dd140" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_5d2af192-8c38-4ee3-a079-8d4b09feb0d0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LesseeOperatingLeaseRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3cd107b4-392c-4fe2-aef9-a45943ae6619" xlink:to="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_5d2af192-8c38-4ee3-a079-8d4b09feb0d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_LesseeOperatingLeaseTerminationPeriod_40181894-950a-42ee-8980-0c4034fc9dee" xlink:href="bsy-20210630.xsd#bsy_LesseeOperatingLeaseTerminationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3cd107b4-392c-4fe2-aef9-a45943ae6619" xlink:to="loc_bsy_LesseeOperatingLeaseTerminationPeriod_40181894-950a-42ee-8980-0c4034fc9dee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_b74bd1d6-2af3-4353-9c49-13192a7a1f1f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3cd107b4-392c-4fe2-aef9-a45943ae6619" xlink:to="loc_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_b74bd1d6-2af3-4353-9c49-13192a7a1f1f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_3053946f-a716-47ea-848c-0f0f399576e2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3cd107b4-392c-4fe2-aef9-a45943ae6619" xlink:to="loc_us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_3053946f-a716-47ea-848c-0f0f399576e2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_LesseeOperatingLeaseLeaseNotYetCommencedLiabilityLeasePayments_96ef06bc-0a9e-4ab0-a717-7ed9d1a76e4f" xlink:href="bsy-20210630.xsd#bsy_LesseeOperatingLeaseLeaseNotYetCommencedLiabilityLeasePayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3cd107b4-392c-4fe2-aef9-a45943ae6619" xlink:to="loc_bsy_LesseeOperatingLeaseLeaseNotYetCommencedLiabilityLeasePayments_96ef06bc-0a9e-4ab0-a717-7ed9d1a76e4f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_337fe471-4c2c-40d2-8979-b25f20a373e8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3cd107b4-392c-4fe2-aef9-a45943ae6619" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_337fe471-4c2c-40d2-8979-b25f20a373e8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_a0fa5432-c844-4057-bb81-33443853f1ad" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_337fe471-4c2c-40d2-8979-b25f20a373e8" xlink:to="loc_srt_RangeAxis_a0fa5432-c844-4057-bb81-33443853f1ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_a0fa5432-c844-4057-bb81-33443853f1ad_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_a0fa5432-c844-4057-bb81-33443853f1ad" xlink:to="loc_srt_RangeMember_a0fa5432-c844-4057-bb81-33443853f1ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_99b8fb9e-b817-4688-8d84-a443c85771c7" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_a0fa5432-c844-4057-bb81-33443853f1ad" xlink:to="loc_srt_RangeMember_99b8fb9e-b817-4688-8d84-a443c85771c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_fa8587cc-d244-4abc-9753-10618e0f2718" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_99b8fb9e-b817-4688-8d84-a443c85771c7" xlink:to="loc_srt_MinimumMember_fa8587cc-d244-4abc-9753-10618e0f2718" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_fdb39c7c-2cd8-4205-9d74-d87873febd43" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_99b8fb9e-b817-4688-8d84-a443c85771c7" xlink:to="loc_srt_MaximumMember_fdb39c7c-2cd8-4205-9d74-d87873febd43" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/LeasesOtherInformationDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#LeasesOtherInformationDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/LeasesOtherInformationDetails" xlink:type="extended" id="ic13a580d6c3c41648176bb5bc83f06a8_LeasesOtherInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_7f4ed186-480e-44b1-9373-8e6b83d3cbe4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeasePayments_9a9478f1-18d9-476b-b6eb-ef1c71008a2b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeasePayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_7f4ed186-480e-44b1-9373-8e6b83d3cbe4" xlink:to="loc_us-gaap_OperatingLeasePayments_9a9478f1-18d9-476b-b6eb-ef1c71008a2b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_3bd5fd84-f7a3-4b0c-9748-a34c1490e669" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_7f4ed186-480e-44b1-9373-8e6b83d3cbe4" xlink:to="loc_us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_3bd5fd84-f7a3-4b0c-9748-a34c1490e669" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCapitalLeaseObligation_1548167a-b8a9-4496-8f6d-2089760b51cd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCapitalLeaseObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_7f4ed186-480e-44b1-9373-8e6b83d3cbe4" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCapitalLeaseObligation_1548167a-b8a9-4496-8f6d-2089760b51cd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_83054fbc-8fb0-4547-ad2e-d51dfa7e564f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_7f4ed186-480e-44b1-9373-8e6b83d3cbe4" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_83054fbc-8fb0-4547-ad2e-d51dfa7e564f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_29034f48-01c9-4eaa-babd-82aeeac4274f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_83054fbc-8fb0-4547-ad2e-d51dfa7e564f" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_29034f48-01c9-4eaa-babd-82aeeac4274f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_29034f48-01c9-4eaa-babd-82aeeac4274f_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_29034f48-01c9-4eaa-babd-82aeeac4274f" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_29034f48-01c9-4eaa-babd-82aeeac4274f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_05b97599-8082-4cad-800e-36b8a3b7f3c7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_29034f48-01c9-4eaa-babd-82aeeac4274f" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_05b97599-8082-4cad-800e-36b8a3b7f3c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_4cd2e1d5-813d-4728-8a55-ec9297e51b43" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_05b97599-8082-4cad-800e-36b8a3b7f3c7" xlink:to="loc_us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_4cd2e1d5-813d-4728-8a55-ec9297e51b43" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/LongTermDebtScheduleofLongTermDebtDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#LongTermDebtScheduleofLongTermDebtDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/LongTermDebtScheduleofLongTermDebtDetails" xlink:type="extended" id="ic7c14aa70ba74f54a9ef0f14fc954b08_LongTermDebtScheduleofLongTermDebtDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_a073c4e6-5f56-4e53-80ec-0fd9c4b53f27" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_329875d0-22d2-4966-9703-fe550d33d81e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a073c4e6-5f56-4e53-80ec-0fd9c4b53f27" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_329875d0-22d2-4966-9703-fe550d33d81e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscount_53bf3814-acc2-4b76-b1a2-e30645530750" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentUnamortizedDiscount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a073c4e6-5f56-4e53-80ec-0fd9c4b53f27" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscount_53bf3814-acc2-4b76-b1a2-e30645530750" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_d35b6f8f-11c4-4005-b60c-2c6901709be0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a073c4e6-5f56-4e53-80ec-0fd9c4b53f27" xlink:to="loc_us-gaap_LongTermDebt_d35b6f8f-11c4-4005-b60c-2c6901709be0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_eeed9161-712b-4247-8dcd-dcbb76fc65cc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a073c4e6-5f56-4e53-80ec-0fd9c4b53f27" xlink:to="loc_us-gaap_DebtInstrumentTable_eeed9161-712b-4247-8dcd-dcbb76fc65cc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_9aed1086-89ab-44c9-87d0-85d46e29f463" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_eeed9161-712b-4247-8dcd-dcbb76fc65cc" xlink:to="loc_us-gaap_CreditFacilityAxis_9aed1086-89ab-44c9-87d0-85d46e29f463" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_9aed1086-89ab-44c9-87d0-85d46e29f463_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_9aed1086-89ab-44c9-87d0-85d46e29f463" xlink:to="loc_us-gaap_CreditFacilityDomain_9aed1086-89ab-44c9-87d0-85d46e29f463_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_601a47bd-754e-4eaa-bac9-753066f7325e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_9aed1086-89ab-44c9-87d0-85d46e29f463" xlink:to="loc_us-gaap_CreditFacilityDomain_601a47bd-754e-4eaa-bac9-753066f7325e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_b147563c-251d-4db8-a99f-2e3ddbd8d79e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_601a47bd-754e-4eaa-bac9-753066f7325e" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_b147563c-251d-4db8-a99f-2e3ddbd8d79e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_777572f1-f720-4915-b823-973b7ce97cb8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_eeed9161-712b-4247-8dcd-dcbb76fc65cc" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_777572f1-f720-4915-b823-973b7ce97cb8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_777572f1-f720-4915-b823-973b7ce97cb8_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_777572f1-f720-4915-b823-973b7ce97cb8" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_777572f1-f720-4915-b823-973b7ce97cb8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_1fdd8f7c-129d-4661-a584-315d6f4e03d5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_777572f1-f720-4915-b823-973b7ce97cb8" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_1fdd8f7c-129d-4661-a584-315d6f4e03d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_d4dee384-8e77-4f24-b6c9-a9981b438253" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_1fdd8f7c-129d-4661-a584-315d6f4e03d5" xlink:to="loc_us-gaap_LineOfCreditMember_d4dee384-8e77-4f24-b6c9-a9981b438253" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_0a84021a-4a51-46e4-b97a-86bb7bd7ee3d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_1fdd8f7c-129d-4661-a584-315d6f4e03d5" xlink:to="loc_us-gaap_ConvertibleDebtMember_0a84021a-4a51-46e4-b97a-86bb7bd7ee3d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_44e4f127-df64-4dc1-8fe0-cef823e8d3a3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_eeed9161-712b-4247-8dcd-dcbb76fc65cc" xlink:to="loc_us-gaap_DebtInstrumentAxis_44e4f127-df64-4dc1-8fe0-cef823e8d3a3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_44e4f127-df64-4dc1-8fe0-cef823e8d3a3_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_44e4f127-df64-4dc1-8fe0-cef823e8d3a3" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_44e4f127-df64-4dc1-8fe0-cef823e8d3a3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_40d06e1e-5bed-4eac-96ea-5f35d42ad3f4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_44e4f127-df64-4dc1-8fe0-cef823e8d3a3" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_40d06e1e-5bed-4eac-96ea-5f35d42ad3f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentySixNotesMember_9c90ec3f-1a09-443f-b1f7-18f3c8cf5ec5" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentySixNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_40d06e1e-5bed-4eac-96ea-5f35d42ad3f4" xlink:to="loc_bsy_TwoThousandTwentySixNotesMember_9c90ec3f-1a09-443f-b1f7-18f3c8cf5ec5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentySevenNotesMember_8d63511b-07a5-41d7-8ffc-7f412d600dc8" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentySevenNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_40d06e1e-5bed-4eac-96ea-5f35d42ad3f4" xlink:to="loc_bsy_TwoThousandTwentySevenNotesMember_8d63511b-07a5-41d7-8ffc-7f412d600dc8" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/LongTermDebtBankCreditFacilityNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#LongTermDebtBankCreditFacilityNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/LongTermDebtBankCreditFacilityNarrativeDetails" xlink:type="extended" id="i4f3cdb0012c74fb682ccdca14a6d6bc7_LongTermDebtBankCreditFacilityNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_922f7d9a-c475-4326-8a12-3b053980660c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_5f37d1e7-bd8c-4d20-b31b-fc659a4aad37" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_922f7d9a-c475-4326-8a12-3b053980660c" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_5f37d1e7-bd8c-4d20-b31b-fc659a4aad37" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WriteOffOfDeferredDebtIssuanceCost_749638d9-adf4-4efb-b65c-95462a464f1c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WriteOffOfDeferredDebtIssuanceCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_922f7d9a-c475-4326-8a12-3b053980660c" xlink:to="loc_us-gaap_WriteOffOfDeferredDebtIssuanceCost_749638d9-adf4-4efb-b65c-95462a464f1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_CapitalizationOfProfessionalFees_1079e959-143a-49a3-9957-38fb4352f4a8" xlink:href="bsy-20210630.xsd#bsy_CapitalizationOfProfessionalFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_922f7d9a-c475-4326-8a12-3b053980660c" xlink:to="loc_bsy_CapitalizationOfProfessionalFees_1079e959-143a-49a3-9957-38fb4352f4a8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_LineOfCreditFacilityAccordionFeatureIncreaseLimit_cc21a5fd-2656-4fd5-aa44-bee1fa38de4a" xlink:href="bsy-20210630.xsd#bsy_LineOfCreditFacilityAccordionFeatureIncreaseLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_922f7d9a-c475-4326-8a12-3b053980660c" xlink:to="loc_bsy_LineOfCreditFacilityAccordionFeatureIncreaseLimit_cc21a5fd-2656-4fd5-aa44-bee1fa38de4a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_58a7e019-e035-4916-9462-dd425cce5113" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_922f7d9a-c475-4326-8a12-3b053980660c" xlink:to="loc_us-gaap_LongTermDebt_58a7e019-e035-4916-9462-dd425cce5113" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_9ad15650-efbe-4583-acdf-4bc1d4840230" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_922f7d9a-c475-4326-8a12-3b053980660c" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_9ad15650-efbe-4583-acdf-4bc1d4840230" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_06960689-12b2-4dc4-b1d4-bc824a30eb55" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_922f7d9a-c475-4326-8a12-3b053980660c" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_06960689-12b2-4dc4-b1d4-bc824a30eb55" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_5871639d-e90c-48ab-9b04-0f3b49e578cc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_922f7d9a-c475-4326-8a12-3b053980660c" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_5871639d-e90c-48ab-9b04-0f3b49e578cc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_LineOfCreditFacilityBorrowingsGuaranteedThroughStockOfForeignSubsidiariesPercentage_e66050f8-7cd1-4b9e-9b8f-121affeeee84" xlink:href="bsy-20210630.xsd#bsy_LineOfCreditFacilityBorrowingsGuaranteedThroughStockOfForeignSubsidiariesPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_922f7d9a-c475-4326-8a12-3b053980660c" xlink:to="loc_bsy_LineOfCreditFacilityBorrowingsGuaranteedThroughStockOfForeignSubsidiariesPercentage_e66050f8-7cd1-4b9e-9b8f-121affeeee84" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtCovenantCrossDefaultsOfOtherDebtThreshold_a97564cc-00a1-4462-80c5-4ce5d59b6def" xlink:href="bsy-20210630.xsd#bsy_DebtCovenantCrossDefaultsOfOtherDebtThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_922f7d9a-c475-4326-8a12-3b053980660c" xlink:to="loc_bsy_DebtCovenantCrossDefaultsOfOtherDebtThreshold_a97564cc-00a1-4462-80c5-4ce5d59b6def" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtCovenantJudgmentDefaultsThreshold_be913cd5-8fce-45ed-978d-266b2a663ef0" xlink:href="bsy-20210630.xsd#bsy_DebtCovenantJudgmentDefaultsThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_922f7d9a-c475-4326-8a12-3b053980660c" xlink:to="loc_bsy_DebtCovenantJudgmentDefaultsThreshold_be913cd5-8fce-45ed-978d-266b2a663ef0" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_6ec4d743-ab61-4671-884c-18cebd8c6c25" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_922f7d9a-c475-4326-8a12-3b053980660c" xlink:to="loc_us-gaap_DebtInstrumentTable_6ec4d743-ab61-4671-884c-18cebd8c6c25" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_d310feb4-77c3-4dd0-910f-d2471e921b91" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_6ec4d743-ab61-4671-884c-18cebd8c6c25" xlink:to="loc_us-gaap_CreditFacilityAxis_d310feb4-77c3-4dd0-910f-d2471e921b91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_d310feb4-77c3-4dd0-910f-d2471e921b91_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_d310feb4-77c3-4dd0-910f-d2471e921b91" xlink:to="loc_us-gaap_CreditFacilityDomain_d310feb4-77c3-4dd0-910f-d2471e921b91_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_f1b84954-f81c-477c-9507-766eb45de304" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_d310feb4-77c3-4dd0-910f-d2471e921b91" xlink:to="loc_us-gaap_CreditFacilityDomain_f1b84954-f81c-477c-9507-766eb45de304" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_0e153312-8f06-4f71-ab9e-93af360423a0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_f1b84954-f81c-477c-9507-766eb45de304" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_0e153312-8f06-4f71-ab9e-93af360423a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_55ce994e-29b3-4b82-b339-0c5aad8d3343" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_f1b84954-f81c-477c-9507-766eb45de304" xlink:to="loc_us-gaap_LetterOfCreditMember_55ce994e-29b3-4b82-b339-0c5aad8d3343" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BridgeLoanMember_171baee0-7a5b-414d-a033-c507da924c27" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BridgeLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_f1b84954-f81c-477c-9507-766eb45de304" xlink:to="loc_us-gaap_BridgeLoanMember_171baee0-7a5b-414d-a033-c507da924c27" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_LettersOfCreditAndSuretyBondsMember_84f580f4-8412-4cd3-8520-7e2e3651209b" xlink:href="bsy-20210630.xsd#bsy_LettersOfCreditAndSuretyBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_f1b84954-f81c-477c-9507-766eb45de304" xlink:to="loc_bsy_LettersOfCreditAndSuretyBondsMember_84f580f4-8412-4cd3-8520-7e2e3651209b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_RevolvingCreditFacilityEuroCurrencyMember_8ce790b2-100a-426e-b978-5cb085a21a8a" xlink:href="bsy-20210630.xsd#bsy_RevolvingCreditFacilityEuroCurrencyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_f1b84954-f81c-477c-9507-766eb45de304" xlink:to="loc_bsy_RevolvingCreditFacilityEuroCurrencyMember_8ce790b2-100a-426e-b978-5cb085a21a8a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_RevolvingCreditFacilityNonEuroCurrencyMember_daa925ad-b49f-4dcc-bf5b-e04079929a50" xlink:href="bsy-20210630.xsd#bsy_RevolvingCreditFacilityNonEuroCurrencyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_f1b84954-f81c-477c-9507-766eb45de304" xlink:to="loc_bsy_RevolvingCreditFacilityNonEuroCurrencyMember_daa925ad-b49f-4dcc-bf5b-e04079929a50" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_66e245aa-73eb-4d9c-88e0-245082f7879b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_6ec4d743-ab61-4671-884c-18cebd8c6c25" xlink:to="loc_us-gaap_DebtInstrumentAxis_66e245aa-73eb-4d9c-88e0-245082f7879b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_66e245aa-73eb-4d9c-88e0-245082f7879b_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_66e245aa-73eb-4d9c-88e0-245082f7879b" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_66e245aa-73eb-4d9c-88e0-245082f7879b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_4f609290-fb8d-4b6f-b66c-d9aa3ffb3c22" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_66e245aa-73eb-4d9c-88e0-245082f7879b" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_4f609290-fb8d-4b6f-b66c-d9aa3ffb3c22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_CreditFacilityMember_3fb96fcf-bad9-42d7-aade-50fb57438124" xlink:href="bsy-20210630.xsd#bsy_CreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_4f609290-fb8d-4b6f-b66c-d9aa3ffb3c22" xlink:to="loc_bsy_CreditFacilityMember_3fb96fcf-bad9-42d7-aade-50fb57438124" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_NewCreditFacilityMember_f6046e72-865e-4e04-8339-2d2433a95064" xlink:href="bsy-20210630.xsd#bsy_NewCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_4f609290-fb8d-4b6f-b66c-d9aa3ffb3c22" xlink:to="loc_bsy_NewCreditFacilityMember_f6046e72-865e-4e04-8339-2d2433a95064" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_9b4c1c27-9108-4340-8cff-a5a0a50dda65" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_6ec4d743-ab61-4671-884c-18cebd8c6c25" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_9b4c1c27-9108-4340-8cff-a5a0a50dda65" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_9b4c1c27-9108-4340-8cff-a5a0a50dda65_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_9b4c1c27-9108-4340-8cff-a5a0a50dda65" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_9b4c1c27-9108-4340-8cff-a5a0a50dda65_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_ac7fd2fe-28ba-49ce-bfe5-5b3d6f797e54" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_9b4c1c27-9108-4340-8cff-a5a0a50dda65" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_ac7fd2fe-28ba-49ce-bfe5-5b3d6f797e54" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_140202f1-b861-45af-b76a-351fc4789ac7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_ac7fd2fe-28ba-49ce-bfe5-5b3d6f797e54" xlink:to="loc_us-gaap_LineOfCreditMember_140202f1-b861-45af-b76a-351fc4789ac7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_3406b2db-2f97-4373-ae93-0a3c4d31ccf0" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_6ec4d743-ab61-4671-884c-18cebd8c6c25" xlink:to="loc_srt_RangeAxis_3406b2db-2f97-4373-ae93-0a3c4d31ccf0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_3406b2db-2f97-4373-ae93-0a3c4d31ccf0_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_3406b2db-2f97-4373-ae93-0a3c4d31ccf0" xlink:to="loc_srt_RangeMember_3406b2db-2f97-4373-ae93-0a3c4d31ccf0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_d9a1b61f-7e66-4c0d-98c4-32ef8c080362" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_3406b2db-2f97-4373-ae93-0a3c4d31ccf0" xlink:to="loc_srt_RangeMember_d9a1b61f-7e66-4c0d-98c4-32ef8c080362" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_386de241-23bc-4e59-8942-06a01c3bb68a" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_d9a1b61f-7e66-4c0d-98c4-32ef8c080362" xlink:to="loc_srt_MinimumMember_386de241-23bc-4e59-8942-06a01c3bb68a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_478bddea-855c-4cf9-9c80-af963fc56558" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_d9a1b61f-7e66-4c0d-98c4-32ef8c080362" xlink:to="loc_srt_MaximumMember_478bddea-855c-4cf9-9c80-af963fc56558" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_c4f42c1b-246e-4052-98d4-16ddb4aaa2be" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_6ec4d743-ab61-4671-884c-18cebd8c6c25" xlink:to="loc_us-gaap_VariableRateAxis_c4f42c1b-246e-4052-98d4-16ddb4aaa2be" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_c4f42c1b-246e-4052-98d4-16ddb4aaa2be_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_c4f42c1b-246e-4052-98d4-16ddb4aaa2be" xlink:to="loc_us-gaap_VariableRateDomain_c4f42c1b-246e-4052-98d4-16ddb4aaa2be_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_0d4128dc-2503-4cc0-b8fd-7cf6a4d20afd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_c4f42c1b-246e-4052-98d4-16ddb4aaa2be" xlink:to="loc_us-gaap_VariableRateDomain_0d4128dc-2503-4cc0-b8fd-7cf6a4d20afd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_b75fe202-fedf-4a86-956f-46ec00d95e37" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_0d4128dc-2503-4cc0-b8fd-7cf6a4d20afd" xlink:to="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_b75fe202-fedf-4a86-956f-46ec00d95e37" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_OvernightBankFundingEffectiveRateMember_469ac9bf-b5dc-432c-96d6-571a5d1cd91c" xlink:href="bsy-20210630.xsd#bsy_OvernightBankFundingEffectiveRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_0d4128dc-2503-4cc0-b8fd-7cf6a4d20afd" xlink:to="loc_bsy_OvernightBankFundingEffectiveRateMember_469ac9bf-b5dc-432c-96d6-571a5d1cd91c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BaseRateMember_921437cd-2a0d-44bc-bb47-83540d2f0f88" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_0d4128dc-2503-4cc0-b8fd-7cf6a4d20afd" xlink:to="loc_us-gaap_BaseRateMember_921437cd-2a0d-44bc-bb47-83540d2f0f88" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/LongTermDebt2026ConvertibleSeniorNotesNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#LongTermDebt2026ConvertibleSeniorNotesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/LongTermDebt2026ConvertibleSeniorNotesNarrativeDetails" xlink:type="extended" id="i8a35c3048a9547449ae8b02129d86532_LongTermDebt2026ConvertibleSeniorNotesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_2807f538-f3f2-47d3-b6a8-aa020aeff4c7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_2807f538-f3f2-47d3-b6a8-aa020aeff4c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_2d41cddb-5cfb-4c09-af41-6157288d9e9b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_2d41cddb-5cfb-4c09-af41-6157288d9e9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDebtIssuanceCosts_c2f9033e-22e4-4b45-b842-bf931a7ca46d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsOfDebtIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:to="loc_us-gaap_PaymentsOfDebtIssuanceCosts_c2f9033e-22e4-4b45-b842-bf931a7ca46d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_2acacad5-5cbe-4758-81ad-109516b3b140" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_2acacad5-5cbe-4758-81ad-109516b3b140" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLinesOfCredit_eafb0f18-70aa-454c-810d-82cae8153a62" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RepaymentsOfLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:to="loc_us-gaap_RepaymentsOfLinesOfCredit_eafb0f18-70aa-454c-810d-82cae8153a62" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_b6520524-e5eb-4542-84a6-b61a5396cd6d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_b6520524-e5eb-4542-84a6-b61a5396cd6d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_9614523c-1585-4997-9258-7efa7b6579d2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentConvertibleThresholdTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_9614523c-1585-4997-9258-7efa7b6579d2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_e9e05035-fd5e-4758-95c5-e2a490176833" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_e9e05035-fd5e-4758-95c5-e2a490176833" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtInstrumentConvertibleThresholdConsecutiveBusinessDays_b8c55715-07e9-4ab3-a11b-ddc70721147e" xlink:href="bsy-20210630.xsd#bsy_DebtInstrumentConvertibleThresholdConsecutiveBusinessDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:to="loc_bsy_DebtInstrumentConvertibleThresholdConsecutiveBusinessDays_b8c55715-07e9-4ab3-a11b-ddc70721147e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtInstrumentConvertibleThresholdConsecutiveTradingDaysAfterThresholdConsecutiveBusinessDays_efd70b9a-2a3f-4b93-9bf8-e1602e6f3448" xlink:href="bsy-20210630.xsd#bsy_DebtInstrumentConvertibleThresholdConsecutiveTradingDaysAfterThresholdConsecutiveBusinessDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:to="loc_bsy_DebtInstrumentConvertibleThresholdConsecutiveTradingDaysAfterThresholdConsecutiveBusinessDays_efd70b9a-2a3f-4b93-9bf8-e1602e6f3448" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_518cdaf7-0a35-4435-a6cf-5bf1495e7b4d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentRedemptionPricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_518cdaf7-0a35-4435-a6cf-5bf1495e7b4d" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtInstrumentConvertibleNumberOfEquityInstrumentsConversionRate_b3739048-200a-42b8-a631-1055e602bfbd" xlink:href="bsy-20210630.xsd#bsy_DebtInstrumentConvertibleNumberOfEquityInstrumentsConversionRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:to="loc_bsy_DebtInstrumentConvertibleNumberOfEquityInstrumentsConversionRate_b3739048-200a-42b8-a631-1055e602bfbd" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_ab945192-a502-4b1e-90d5-0de35218de32" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_ab945192-a502-4b1e-90d5-0de35218de32" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_NumberOfTradingDaysAfterMaturityDateDebtRedeemable_847505c8-1fcf-4d6b-8e73-49fdfe3a0acf" xlink:href="bsy-20210630.xsd#bsy_NumberOfTradingDaysAfterMaturityDateDebtRedeemable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:to="loc_bsy_NumberOfTradingDaysAfterMaturityDateDebtRedeemable_847505c8-1fcf-4d6b-8e73-49fdfe3a0acf" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtInstrumentConvertibleSharePriceThresholdAdjustmentToConversionRate_15549bc2-2150-4c0e-9477-88ad0192de62" xlink:href="bsy-20210630.xsd#bsy_DebtInstrumentConvertibleSharePriceThresholdAdjustmentToConversionRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:to="loc_bsy_DebtInstrumentConvertibleSharePriceThresholdAdjustmentToConversionRate_15549bc2-2150-4c0e-9477-88ad0192de62" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtCovenantPercentOfNoteHoldersThresholdByAmountOfPrincipalOutstanding_2505d947-f23f-4d7b-a597-517b7d887dbf" xlink:href="bsy-20210630.xsd#bsy_DebtCovenantPercentOfNoteHoldersThresholdByAmountOfPrincipalOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:to="loc_bsy_DebtCovenantPercentOfNoteHoldersThresholdByAmountOfPrincipalOutstanding_2505d947-f23f-4d7b-a597-517b7d887dbf" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_7e9f97ea-2759-4ec6-b787-697946185965" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_7e9f97ea-2759-4ec6-b787-697946185965" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_e98dc2b9-eda8-43f3-89ac-eeb5f2ac1057" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_503dddc2-12f8-48b6-beeb-28dadb7b35d0" xlink:to="loc_us-gaap_DebtInstrumentTable_e98dc2b9-eda8-43f3-89ac-eeb5f2ac1057" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_42637a52-3b63-4b05-83d6-c4daa8903d67" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_e98dc2b9-eda8-43f3-89ac-eeb5f2ac1057" xlink:to="loc_us-gaap_DebtInstrumentAxis_42637a52-3b63-4b05-83d6-c4daa8903d67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_42637a52-3b63-4b05-83d6-c4daa8903d67_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_42637a52-3b63-4b05-83d6-c4daa8903d67" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_42637a52-3b63-4b05-83d6-c4daa8903d67_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_2e7a4790-6c1f-4b30-b880-6b17cf5532f9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_42637a52-3b63-4b05-83d6-c4daa8903d67" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_2e7a4790-6c1f-4b30-b880-6b17cf5532f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentySixNotesMember_cdfb2462-c695-429c-b56d-500d281f7adb" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentySixNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_2e7a4790-6c1f-4b30-b880-6b17cf5532f9" xlink:to="loc_bsy_TwoThousandTwentySixNotesMember_cdfb2462-c695-429c-b56d-500d281f7adb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_bdacb020-3d86-4d57-80b0-469e58f3c036" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_e98dc2b9-eda8-43f3-89ac-eeb5f2ac1057" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_bdacb020-3d86-4d57-80b0-469e58f3c036" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_bdacb020-3d86-4d57-80b0-469e58f3c036_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_bdacb020-3d86-4d57-80b0-469e58f3c036" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_bdacb020-3d86-4d57-80b0-469e58f3c036_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_0ffe3152-15b5-48a0-914f-89981efdce00" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_bdacb020-3d86-4d57-80b0-469e58f3c036" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_0ffe3152-15b5-48a0-914f-89981efdce00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_fc2f979e-cafa-48a5-bcf8-0030e5ff8a8e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_0ffe3152-15b5-48a0-914f-89981efdce00" xlink:to="loc_us-gaap_ConvertibleDebtMember_fc2f979e-cafa-48a5-bcf8-0030e5ff8a8e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtInstrumentConvertibleTermsOfConversionAxis_0c532318-c47f-473b-8a89-c0c327a60263" xlink:href="bsy-20210630.xsd#bsy_DebtInstrumentConvertibleTermsOfConversionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_e98dc2b9-eda8-43f3-89ac-eeb5f2ac1057" xlink:to="loc_bsy_DebtInstrumentConvertibleTermsOfConversionAxis_0c532318-c47f-473b-8a89-c0c327a60263" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtInstrumentConvertibleTermsOfConversionDomain_0c532318-c47f-473b-8a89-c0c327a60263_default" xlink:href="bsy-20210630.xsd#bsy_DebtInstrumentConvertibleTermsOfConversionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_bsy_DebtInstrumentConvertibleTermsOfConversionAxis_0c532318-c47f-473b-8a89-c0c327a60263" xlink:to="loc_bsy_DebtInstrumentConvertibleTermsOfConversionDomain_0c532318-c47f-473b-8a89-c0c327a60263_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtInstrumentConvertibleTermsOfConversionDomain_64f76cd4-b310-4a9e-a7a9-8881ff083d4e" xlink:href="bsy-20210630.xsd#bsy_DebtInstrumentConvertibleTermsOfConversionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_bsy_DebtInstrumentConvertibleTermsOfConversionAxis_0c532318-c47f-473b-8a89-c0c327a60263" xlink:to="loc_bsy_DebtInstrumentConvertibleTermsOfConversionDomain_64f76cd4-b310-4a9e-a7a9-8881ff083d4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtConversionTermsOneMember_7ff16a35-e355-46f0-b667-4026600fc53a" xlink:href="bsy-20210630.xsd#bsy_DebtConversionTermsOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_DebtInstrumentConvertibleTermsOfConversionDomain_64f76cd4-b310-4a9e-a7a9-8881ff083d4e" xlink:to="loc_bsy_DebtConversionTermsOneMember_7ff16a35-e355-46f0-b667-4026600fc53a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtConversionTermsTwoMember_14c7f1c7-e4a1-448e-ae69-579b7e8b46b3" xlink:href="bsy-20210630.xsd#bsy_DebtConversionTermsTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_DebtInstrumentConvertibleTermsOfConversionDomain_64f76cd4-b310-4a9e-a7a9-8881ff083d4e" xlink:to="loc_bsy_DebtConversionTermsTwoMember_14c7f1c7-e4a1-448e-ae69-579b7e8b46b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_451638d2-2d38-4237-be87-af269d476bb1" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_e98dc2b9-eda8-43f3-89ac-eeb5f2ac1057" xlink:to="loc_srt_RangeAxis_451638d2-2d38-4237-be87-af269d476bb1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_451638d2-2d38-4237-be87-af269d476bb1_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_451638d2-2d38-4237-be87-af269d476bb1" xlink:to="loc_srt_RangeMember_451638d2-2d38-4237-be87-af269d476bb1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_c7fc68a3-178b-4dfd-b4bb-52b9862b03a0" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_451638d2-2d38-4237-be87-af269d476bb1" xlink:to="loc_srt_RangeMember_c7fc68a3-178b-4dfd-b4bb-52b9862b03a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_840f9510-5e95-439c-81db-fbf5e9196b41" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c7fc68a3-178b-4dfd-b4bb-52b9862b03a0" xlink:to="loc_srt_MinimumMember_840f9510-5e95-439c-81db-fbf5e9196b41" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_a5be882f-1fc4-407f-a623-03f1862e365d" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c7fc68a3-178b-4dfd-b4bb-52b9862b03a0" xlink:to="loc_srt_MaximumMember_a5be882f-1fc4-407f-a623-03f1862e365d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_01c9618e-abdd-4f3b-8251-477597e04ef5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_e98dc2b9-eda8-43f3-89ac-eeb5f2ac1057" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_01c9618e-abdd-4f3b-8251-477597e04ef5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_01c9618e-abdd-4f3b-8251-477597e04ef5_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_01c9618e-abdd-4f3b-8251-477597e04ef5" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_01c9618e-abdd-4f3b-8251-477597e04ef5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_c7e2f65c-9d91-4f40-bd00-1859eadf1f6f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_01c9618e-abdd-4f3b-8251-477597e04ef5" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_c7e2f65c-9d91-4f40-bd00-1859eadf1f6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableMember_0954ebda-7714-4eef-a984-8e8d1fde7f42" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountsPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_c7e2f65c-9d91-4f40-bd00-1859eadf1f6f" xlink:to="loc_us-gaap_AccountsPayableMember_0954ebda-7714-4eef-a984-8e8d1fde7f42" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_AccruedLiabilitiesCurrentMember_4e43fc85-2d91-48b7-9a97-758604912930" xlink:href="bsy-20210630.xsd#bsy_AccruedLiabilitiesCurrentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_c7e2f65c-9d91-4f40-bd00-1859eadf1f6f" xlink:to="loc_bsy_AccruedLiabilitiesCurrentMember_4e43fc85-2d91-48b7-9a97-758604912930" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/LongTermDebt2026NotesCappedCallOptionsNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#LongTermDebt2026NotesCappedCallOptionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/LongTermDebt2026NotesCappedCallOptionsNarrativeDetails" xlink:type="extended" id="iedf3d7ff1bb146b6ad88a8d6c0b48706_LongTermDebt2026NotesCappedCallOptionsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_9f04272a-fc7f-42dc-8d09-7df89dedc015" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_CappedCallOptionsExpense_057a31c3-21b2-452c-99af-2342b6c31b40" xlink:href="bsy-20210630.xsd#bsy_CappedCallOptionsExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_9f04272a-fc7f-42dc-8d09-7df89dedc015" xlink:to="loc_bsy_CappedCallOptionsExpense_057a31c3-21b2-452c-99af-2342b6c31b40" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityStrikePrice1_ac8cb690-d503-4b76-9e72-a6eb14673ac6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OptionIndexedToIssuersEquityStrikePrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_9f04272a-fc7f-42dc-8d09-7df89dedc015" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquityStrikePrice1_ac8cb690-d503-4b76-9e72-a6eb14673ac6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_OptionIndexedToIssuersEquityStrikePricePremiumOverSharePricePercentage_3768bcab-2227-4313-b477-f7cb0f1a0d20" xlink:href="bsy-20210630.xsd#bsy_OptionIndexedToIssuersEquityStrikePricePremiumOverSharePricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_9f04272a-fc7f-42dc-8d09-7df89dedc015" xlink:to="loc_bsy_OptionIndexedToIssuersEquityStrikePricePremiumOverSharePricePercentage_3768bcab-2227-4313-b477-f7cb0f1a0d20" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_a3d189f8-85e6-415c-a20e-5cb6548c9cc1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_9f04272a-fc7f-42dc-8d09-7df89dedc015" xlink:to="loc_us-gaap_DebtInstrumentTable_a3d189f8-85e6-415c-a20e-5cb6548c9cc1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_3f295b4e-a6b2-4ab6-8bfd-f984300cce29" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a3d189f8-85e6-415c-a20e-5cb6548c9cc1" xlink:to="loc_us-gaap_DebtInstrumentAxis_3f295b4e-a6b2-4ab6-8bfd-f984300cce29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_3f295b4e-a6b2-4ab6-8bfd-f984300cce29_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_3f295b4e-a6b2-4ab6-8bfd-f984300cce29" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_3f295b4e-a6b2-4ab6-8bfd-f984300cce29_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_7182148a-7861-4514-b12f-148217d79544" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_3f295b4e-a6b2-4ab6-8bfd-f984300cce29" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_7182148a-7861-4514-b12f-148217d79544" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentySixNotesMember_c72c83fc-6d9a-48fc-9f09-8be707e4dea4" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentySixNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_7182148a-7861-4514-b12f-148217d79544" xlink:to="loc_bsy_TwoThousandTwentySixNotesMember_c72c83fc-6d9a-48fc-9f09-8be707e4dea4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentySevenNotesMember_9d7a8d7d-0a86-4e2a-81fa-a5f8a7376123" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentySevenNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_7182148a-7861-4514-b12f-148217d79544" xlink:to="loc_bsy_TwoThousandTwentySevenNotesMember_9d7a8d7d-0a86-4e2a-81fa-a5f8a7376123" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_727e554f-c1de-4208-83c6-2c5bf218ffdd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a3d189f8-85e6-415c-a20e-5cb6548c9cc1" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_727e554f-c1de-4208-83c6-2c5bf218ffdd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_727e554f-c1de-4208-83c6-2c5bf218ffdd_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_727e554f-c1de-4208-83c6-2c5bf218ffdd" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_727e554f-c1de-4208-83c6-2c5bf218ffdd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_c75a15cb-5f90-4252-a619-26c0a37a4bfe" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_727e554f-c1de-4208-83c6-2c5bf218ffdd" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_c75a15cb-5f90-4252-a619-26c0a37a4bfe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_c47ab60f-2fcc-46fc-a0b1-d1a15860017b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_c75a15cb-5f90-4252-a619-26c0a37a4bfe" xlink:to="loc_us-gaap_ConvertibleDebtMember_c47ab60f-2fcc-46fc-a0b1-d1a15860017b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/LongTermDebt2027ConvertibleSeniorNotesNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#LongTermDebt2027ConvertibleSeniorNotesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/LongTermDebt2027ConvertibleSeniorNotesNarrativeDetails" xlink:type="extended" id="ib49882c706504c9893342c9cdc212afa_LongTermDebt2027ConvertibleSeniorNotesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_242b9fc6-a739-4ab4-8fe2-d193db0e9c5d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_242b9fc6-a739-4ab4-8fe2-d193db0e9c5d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_1f040d35-87f6-45fd-8aa2-4defa87820b9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_1f040d35-87f6-45fd-8aa2-4defa87820b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDebtIssuanceCosts_3efb20ef-5229-4dee-96ac-cbe08cf5a803" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsOfDebtIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:to="loc_us-gaap_PaymentsOfDebtIssuanceCosts_3efb20ef-5229-4dee-96ac-cbe08cf5a803" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_36970d47-6100-4f6c-80c3-829b317886ca" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_36970d47-6100-4f6c-80c3-829b317886ca" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLinesOfCredit_eb71f8d4-cb82-4f09-affa-61d30353d52d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RepaymentsOfLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:to="loc_us-gaap_RepaymentsOfLinesOfCredit_eb71f8d4-cb82-4f09-affa-61d30353d52d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_8eb35f7f-a57c-4965-870e-db1041859114" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_8eb35f7f-a57c-4965-870e-db1041859114" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_e5c34f99-d5ed-420e-9ead-a07491498f58" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentConvertibleThresholdTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_e5c34f99-d5ed-420e-9ead-a07491498f58" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_e86ed919-21b0-48d6-ae75-566285f2f5fe" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_e86ed919-21b0-48d6-ae75-566285f2f5fe" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtInstrumentConvertibleThresholdConsecutiveBusinessDays_60e1ebe4-cdd7-4286-8e1c-0ae269856f21" xlink:href="bsy-20210630.xsd#bsy_DebtInstrumentConvertibleThresholdConsecutiveBusinessDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:to="loc_bsy_DebtInstrumentConvertibleThresholdConsecutiveBusinessDays_60e1ebe4-cdd7-4286-8e1c-0ae269856f21" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtInstrumentConvertibleThresholdConsecutiveTradingDaysAfterThresholdConsecutiveBusinessDays_6bcc81dd-cfe4-4aed-be87-fab281f23407" xlink:href="bsy-20210630.xsd#bsy_DebtInstrumentConvertibleThresholdConsecutiveTradingDaysAfterThresholdConsecutiveBusinessDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:to="loc_bsy_DebtInstrumentConvertibleThresholdConsecutiveTradingDaysAfterThresholdConsecutiveBusinessDays_6bcc81dd-cfe4-4aed-be87-fab281f23407" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_e4bba4dc-1e91-46df-b50a-b60498d3744b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentRedemptionPricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_e4bba4dc-1e91-46df-b50a-b60498d3744b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtInstrumentConvertibleNumberOfEquityInstrumentsConversionRate_be7fcfd0-3432-4c2f-b695-909c60c83119" xlink:href="bsy-20210630.xsd#bsy_DebtInstrumentConvertibleNumberOfEquityInstrumentsConversionRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:to="loc_bsy_DebtInstrumentConvertibleNumberOfEquityInstrumentsConversionRate_be7fcfd0-3432-4c2f-b695-909c60c83119" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_75a35e87-38ea-461e-9e0c-fe2553eddde0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_75a35e87-38ea-461e-9e0c-fe2553eddde0" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_NumberOfTradingDaysAfterMaturityDateDebtRedeemable_ab596e89-1d9d-4ac9-8fa0-549d24e2a160" xlink:href="bsy-20210630.xsd#bsy_NumberOfTradingDaysAfterMaturityDateDebtRedeemable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:to="loc_bsy_NumberOfTradingDaysAfterMaturityDateDebtRedeemable_ab596e89-1d9d-4ac9-8fa0-549d24e2a160" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtInstrumentConvertibleSharePriceThresholdAdjustmentToConversionRate_1b0aa6a7-0f0a-4608-80df-6ecbe2b33faf" xlink:href="bsy-20210630.xsd#bsy_DebtInstrumentConvertibleSharePriceThresholdAdjustmentToConversionRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:to="loc_bsy_DebtInstrumentConvertibleSharePriceThresholdAdjustmentToConversionRate_1b0aa6a7-0f0a-4608-80df-6ecbe2b33faf" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtCovenantPercentOfNoteHoldersThresholdByAmountOfPrincipalOutstanding_0fceab20-7c16-484b-9de9-d8481a12da89" xlink:href="bsy-20210630.xsd#bsy_DebtCovenantPercentOfNoteHoldersThresholdByAmountOfPrincipalOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:to="loc_bsy_DebtCovenantPercentOfNoteHoldersThresholdByAmountOfPrincipalOutstanding_0fceab20-7c16-484b-9de9-d8481a12da89" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_56e53b83-4104-4989-b707-a7a0fa14c09f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_56e53b83-4104-4989-b707-a7a0fa14c09f" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_30e81ddd-6603-471f-9d28-bcff299adc2b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f2a42f36-a8fa-46a4-96b8-7dd708003d7d" xlink:to="loc_us-gaap_DebtInstrumentTable_30e81ddd-6603-471f-9d28-bcff299adc2b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_44d18a02-6fb4-4a2c-afa4-ffd9192aea46" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_30e81ddd-6603-471f-9d28-bcff299adc2b" xlink:to="loc_us-gaap_DebtInstrumentAxis_44d18a02-6fb4-4a2c-afa4-ffd9192aea46" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_44d18a02-6fb4-4a2c-afa4-ffd9192aea46_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_44d18a02-6fb4-4a2c-afa4-ffd9192aea46" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_44d18a02-6fb4-4a2c-afa4-ffd9192aea46_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_bb68b9ee-a78b-4309-8609-7a35a27476f0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_44d18a02-6fb4-4a2c-afa4-ffd9192aea46" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_bb68b9ee-a78b-4309-8609-7a35a27476f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentySevenNotesMember_f93bd048-d6b2-4527-b597-8a7dfb6fd0bd" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentySevenNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_bb68b9ee-a78b-4309-8609-7a35a27476f0" xlink:to="loc_bsy_TwoThousandTwentySevenNotesMember_f93bd048-d6b2-4527-b597-8a7dfb6fd0bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentySixNotesMember_8f305b67-8e0a-44e1-aaf3-26a1f9818d87" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentySixNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_bb68b9ee-a78b-4309-8609-7a35a27476f0" xlink:to="loc_bsy_TwoThousandTwentySixNotesMember_8f305b67-8e0a-44e1-aaf3-26a1f9818d87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_6c1ddf3b-ef03-48b6-9107-2add624c654b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_30e81ddd-6603-471f-9d28-bcff299adc2b" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_6c1ddf3b-ef03-48b6-9107-2add624c654b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_6c1ddf3b-ef03-48b6-9107-2add624c654b_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_6c1ddf3b-ef03-48b6-9107-2add624c654b" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_6c1ddf3b-ef03-48b6-9107-2add624c654b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_5bc3fd2c-2f45-4a06-a05b-dc8ed1f9731a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_6c1ddf3b-ef03-48b6-9107-2add624c654b" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_5bc3fd2c-2f45-4a06-a05b-dc8ed1f9731a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_120a583d-37d5-438a-8ce4-453e04e7ce54" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_5bc3fd2c-2f45-4a06-a05b-dc8ed1f9731a" xlink:to="loc_us-gaap_ConvertibleDebtMember_120a583d-37d5-438a-8ce4-453e04e7ce54" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_54b76688-5426-404b-91da-072d7586690e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_30e81ddd-6603-471f-9d28-bcff299adc2b" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_54b76688-5426-404b-91da-072d7586690e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_54b76688-5426-404b-91da-072d7586690e_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_54b76688-5426-404b-91da-072d7586690e" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_54b76688-5426-404b-91da-072d7586690e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_f0a2531e-548c-4194-b9ec-4f2611035958" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_54b76688-5426-404b-91da-072d7586690e" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_f0a2531e-548c-4194-b9ec-4f2611035958" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableMember_19a2d970-eef6-461d-9c54-fb2ca02c58d2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountsPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_f0a2531e-548c-4194-b9ec-4f2611035958" xlink:to="loc_us-gaap_AccountsPayableMember_19a2d970-eef6-461d-9c54-fb2ca02c58d2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_AccruedLiabilitiesCurrentMember_bb64d221-8678-4433-9dbe-0e6a39101525" xlink:href="bsy-20210630.xsd#bsy_AccruedLiabilitiesCurrentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_f0a2531e-548c-4194-b9ec-4f2611035958" xlink:to="loc_bsy_AccruedLiabilitiesCurrentMember_bb64d221-8678-4433-9dbe-0e6a39101525" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtInstrumentConvertibleTermsOfConversionAxis_605ef5cb-4232-4e69-83c8-262bd7b5a800" xlink:href="bsy-20210630.xsd#bsy_DebtInstrumentConvertibleTermsOfConversionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_30e81ddd-6603-471f-9d28-bcff299adc2b" xlink:to="loc_bsy_DebtInstrumentConvertibleTermsOfConversionAxis_605ef5cb-4232-4e69-83c8-262bd7b5a800" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtInstrumentConvertibleTermsOfConversionDomain_605ef5cb-4232-4e69-83c8-262bd7b5a800_default" xlink:href="bsy-20210630.xsd#bsy_DebtInstrumentConvertibleTermsOfConversionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_bsy_DebtInstrumentConvertibleTermsOfConversionAxis_605ef5cb-4232-4e69-83c8-262bd7b5a800" xlink:to="loc_bsy_DebtInstrumentConvertibleTermsOfConversionDomain_605ef5cb-4232-4e69-83c8-262bd7b5a800_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtInstrumentConvertibleTermsOfConversionDomain_db9ab836-5bb4-45d1-b83a-52d37ecf78e1" xlink:href="bsy-20210630.xsd#bsy_DebtInstrumentConvertibleTermsOfConversionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_bsy_DebtInstrumentConvertibleTermsOfConversionAxis_605ef5cb-4232-4e69-83c8-262bd7b5a800" xlink:to="loc_bsy_DebtInstrumentConvertibleTermsOfConversionDomain_db9ab836-5bb4-45d1-b83a-52d37ecf78e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtConversionTermsOneMember_93533105-e117-4932-ad60-32ef02d5c6f8" xlink:href="bsy-20210630.xsd#bsy_DebtConversionTermsOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_DebtInstrumentConvertibleTermsOfConversionDomain_db9ab836-5bb4-45d1-b83a-52d37ecf78e1" xlink:to="loc_bsy_DebtConversionTermsOneMember_93533105-e117-4932-ad60-32ef02d5c6f8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DebtConversionTermsTwoMember_0c4deded-4172-4be0-884b-da5667a0b766" xlink:href="bsy-20210630.xsd#bsy_DebtConversionTermsTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_DebtInstrumentConvertibleTermsOfConversionDomain_db9ab836-5bb4-45d1-b83a-52d37ecf78e1" xlink:to="loc_bsy_DebtConversionTermsTwoMember_0c4deded-4172-4be0-884b-da5667a0b766" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_5a342fd0-0740-47b6-ac2f-5e7c7bfc4728" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_30e81ddd-6603-471f-9d28-bcff299adc2b" xlink:to="loc_srt_RangeAxis_5a342fd0-0740-47b6-ac2f-5e7c7bfc4728" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_5a342fd0-0740-47b6-ac2f-5e7c7bfc4728_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_5a342fd0-0740-47b6-ac2f-5e7c7bfc4728" xlink:to="loc_srt_RangeMember_5a342fd0-0740-47b6-ac2f-5e7c7bfc4728_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_c414d789-c91d-4f44-9ed8-9be683fde71e" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_5a342fd0-0740-47b6-ac2f-5e7c7bfc4728" xlink:to="loc_srt_RangeMember_c414d789-c91d-4f44-9ed8-9be683fde71e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_dfc6615f-7199-450b-b5d0-2e78863e52ed" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c414d789-c91d-4f44-9ed8-9be683fde71e" xlink:to="loc_srt_MinimumMember_dfc6615f-7199-450b-b5d0-2e78863e52ed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_6d02034a-5a3d-4593-baaf-b5e28c580d20" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c414d789-c91d-4f44-9ed8-9be683fde71e" xlink:to="loc_srt_MaximumMember_6d02034a-5a3d-4593-baaf-b5e28c580d20" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/LongTermDebt2027NotesCappedCallOptionsNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#LongTermDebt2027NotesCappedCallOptionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/LongTermDebt2027NotesCappedCallOptionsNarrativeDetails" xlink:type="extended" id="i5c8bdb5493e743c2ac9bead548060812_LongTermDebt2027NotesCappedCallOptionsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_deaf94e9-c997-490d-8ce2-919fb322196e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_CappedCallOptionsExpense_3344779d-5df3-43b2-8efe-294b2446a82f" xlink:href="bsy-20210630.xsd#bsy_CappedCallOptionsExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_deaf94e9-c997-490d-8ce2-919fb322196e" xlink:to="loc_bsy_CappedCallOptionsExpense_3344779d-5df3-43b2-8efe-294b2446a82f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityStrikePrice1_1731c0b8-da6d-4668-abbf-f5b5cf7a0437" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OptionIndexedToIssuersEquityStrikePrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_deaf94e9-c997-490d-8ce2-919fb322196e" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquityStrikePrice1_1731c0b8-da6d-4668-abbf-f5b5cf7a0437" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_OptionIndexedToIssuersEquityStrikePricePremiumOverSharePricePercentage_256277e1-77b5-4f76-9dd6-f76592564633" xlink:href="bsy-20210630.xsd#bsy_OptionIndexedToIssuersEquityStrikePricePremiumOverSharePricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_deaf94e9-c997-490d-8ce2-919fb322196e" xlink:to="loc_bsy_OptionIndexedToIssuersEquityStrikePricePremiumOverSharePricePercentage_256277e1-77b5-4f76-9dd6-f76592564633" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_0cdafc66-cca7-4998-9c98-530890e64547" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_deaf94e9-c997-490d-8ce2-919fb322196e" xlink:to="loc_us-gaap_DebtInstrumentTable_0cdafc66-cca7-4998-9c98-530890e64547" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_cb0ebab4-f546-49f7-b473-a9ef421fa662" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_0cdafc66-cca7-4998-9c98-530890e64547" xlink:to="loc_us-gaap_DebtInstrumentAxis_cb0ebab4-f546-49f7-b473-a9ef421fa662" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_cb0ebab4-f546-49f7-b473-a9ef421fa662_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_cb0ebab4-f546-49f7-b473-a9ef421fa662" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_cb0ebab4-f546-49f7-b473-a9ef421fa662_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_165f679b-cb51-45b8-8c66-dcc9c3aaaab0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_cb0ebab4-f546-49f7-b473-a9ef421fa662" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_165f679b-cb51-45b8-8c66-dcc9c3aaaab0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentySevenNotesMember_0aa6d157-3b27-4921-8d82-846d8565f30e" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentySevenNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_165f679b-cb51-45b8-8c66-dcc9c3aaaab0" xlink:to="loc_bsy_TwoThousandTwentySevenNotesMember_0aa6d157-3b27-4921-8d82-846d8565f30e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_ab4ee298-dbb0-423d-bd7b-326d716fe5d6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_0cdafc66-cca7-4998-9c98-530890e64547" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_ab4ee298-dbb0-423d-bd7b-326d716fe5d6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_ab4ee298-dbb0-423d-bd7b-326d716fe5d6_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_ab4ee298-dbb0-423d-bd7b-326d716fe5d6" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_ab4ee298-dbb0-423d-bd7b-326d716fe5d6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_70858bce-6a27-4516-96f8-a6e0213f9d92" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_ab4ee298-dbb0-423d-bd7b-326d716fe5d6" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_70858bce-6a27-4516-96f8-a6e0213f9d92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_f412a41c-2c6d-4cdd-8304-bd49b4d5ede8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_70858bce-6a27-4516-96f8-a6e0213f9d92" xlink:to="loc_us-gaap_ConvertibleDebtMember_f412a41c-2c6d-4cdd-8304-bd49b4d5ede8" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/LongTermDebtScheduleofInterestExpenseDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#LongTermDebtScheduleofInterestExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/LongTermDebtScheduleofInterestExpenseDetails" xlink:type="extended" id="ica76fdc9ef0b485686cadce80bfbf875_LongTermDebtScheduleofInterestExpenseDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_7177e5b5-8306-4719-95aa-1f2daa85bcb7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebtExcludingAmortization_e40a6943-8875-4fa9-93f5-28ceb53c6d1d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestExpenseDebtExcludingAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7177e5b5-8306-4719-95aa-1f2daa85bcb7" xlink:to="loc_us-gaap_InterestExpenseDebtExcludingAmortization_e40a6943-8875-4fa9-93f5-28ceb53c6d1d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_InterestExpenseDerivatives_26cb94a4-5272-4fbd-b78c-596a457d24df" xlink:href="bsy-20210630.xsd#bsy_InterestExpenseDerivatives"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7177e5b5-8306-4719-95aa-1f2daa85bcb7" xlink:to="loc_bsy_InterestExpenseDerivatives_26cb94a4-5272-4fbd-b78c-596a457d24df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_fb3238c9-90b7-4a19-8f94-6c4c96f13fa1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AmortizationOfFinancingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7177e5b5-8306-4719-95aa-1f2daa85bcb7" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_fb3238c9-90b7-4a19-8f94-6c4c96f13fa1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_1d4273b4-658d-4c30-8918-ce54e323d40a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7177e5b5-8306-4719-95aa-1f2daa85bcb7" xlink:to="loc_us-gaap_InterestExpenseDebt_1d4273b4-658d-4c30-8918-ce54e323d40a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseOther_76fb0dbd-c156-4772-822d-22f9171de4b5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestExpenseOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7177e5b5-8306-4719-95aa-1f2daa85bcb7" xlink:to="loc_us-gaap_InterestExpenseOther_76fb0dbd-c156-4772-822d-22f9171de4b5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_b60fd9a0-346c-4c25-b38e-a2c65abf7734" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7177e5b5-8306-4719-95aa-1f2daa85bcb7" xlink:to="loc_us-gaap_InterestExpense_b60fd9a0-346c-4c25-b38e-a2c65abf7734" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtWeightedAverageInterestRateOverTime_dc536fba-c5be-4558-a28d-822fc6227c21" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermDebtWeightedAverageInterestRateOverTime"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7177e5b5-8306-4719-95aa-1f2daa85bcb7" xlink:to="loc_us-gaap_LongTermDebtWeightedAverageInterestRateOverTime_dc536fba-c5be-4558-a28d-822fc6227c21" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_c1a73f7a-b629-4676-a038-db49244797d0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7177e5b5-8306-4719-95aa-1f2daa85bcb7" xlink:to="loc_us-gaap_DebtInstrumentTable_c1a73f7a-b629-4676-a038-db49244797d0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_366bb2ca-1de4-4604-bfb2-7372cc67f3b3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_c1a73f7a-b629-4676-a038-db49244797d0" xlink:to="loc_us-gaap_DebtInstrumentAxis_366bb2ca-1de4-4604-bfb2-7372cc67f3b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_366bb2ca-1de4-4604-bfb2-7372cc67f3b3_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_366bb2ca-1de4-4604-bfb2-7372cc67f3b3" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_366bb2ca-1de4-4604-bfb2-7372cc67f3b3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_96165436-1e1b-4831-819a-2eaa6d9d3d78" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_366bb2ca-1de4-4604-bfb2-7372cc67f3b3" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_96165436-1e1b-4831-819a-2eaa6d9d3d78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_CreditFacilityMember_c2b1a981-e135-42ae-864c-e7dd3b493a6e" xlink:href="bsy-20210630.xsd#bsy_CreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_96165436-1e1b-4831-819a-2eaa6d9d3d78" xlink:to="loc_bsy_CreditFacilityMember_c2b1a981-e135-42ae-864c-e7dd3b493a6e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentySixNotesMember_f2627262-2ede-4965-8685-c590abefc79f" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentySixNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_96165436-1e1b-4831-819a-2eaa6d9d3d78" xlink:to="loc_bsy_TwoThousandTwentySixNotesMember_f2627262-2ede-4965-8685-c590abefc79f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentySevenNotesMember_c7730a15-c892-40d3-9db6-632ee5974b6f" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentySevenNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_96165436-1e1b-4831-819a-2eaa6d9d3d78" xlink:to="loc_bsy_TwoThousandTwentySevenNotesMember_c7730a15-c892-40d3-9db6-632ee5974b6f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_49a5a3eb-a1dd-4baf-a2c6-bc9c4c239779" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_c1a73f7a-b629-4676-a038-db49244797d0" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_49a5a3eb-a1dd-4baf-a2c6-bc9c4c239779" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_49a5a3eb-a1dd-4baf-a2c6-bc9c4c239779_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_49a5a3eb-a1dd-4baf-a2c6-bc9c4c239779" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_49a5a3eb-a1dd-4baf-a2c6-bc9c4c239779_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_46792df7-d563-4a44-b95b-bea54f6821d0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_49a5a3eb-a1dd-4baf-a2c6-bc9c4c239779" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_46792df7-d563-4a44-b95b-bea54f6821d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_290d5517-7325-4eeb-88c9-05107bc14062" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_46792df7-d563-4a44-b95b-bea54f6821d0" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_290d5517-7325-4eeb-88c9-05107bc14062" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_84d573e2-692d-41dd-97c6-1f75951c06c4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_46792df7-d563-4a44-b95b-bea54f6821d0" xlink:to="loc_us-gaap_ConvertibleDebtMember_84d573e2-692d-41dd-97c6-1f75951c06c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_8b970535-d420-43f2-8af4-cd53f51764ee" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_c1a73f7a-b629-4676-a038-db49244797d0" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_8b970535-d420-43f2-8af4-cd53f51764ee" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_8b970535-d420-43f2-8af4-cd53f51764ee_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_8b970535-d420-43f2-8af4-cd53f51764ee" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_8b970535-d420-43f2-8af4-cd53f51764ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_37b69561-9375-48d8-b7d5-48355169eb68" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_8b970535-d420-43f2-8af4-cd53f51764ee" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_37b69561-9375-48d8-b7d5-48355169eb68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_fa3f5fb8-3181-42f5-a629-a62e0a4978f7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_37b69561-9375-48d8-b7d5-48355169eb68" xlink:to="loc_us-gaap_InterestRateSwapMember_fa3f5fb8-3181-42f5-a629-a62e0a4978f7" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/LongTermDebtAdditionalNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#LongTermDebtAdditionalNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/LongTermDebtAdditionalNarrativeDetails" xlink:type="extended" id="ic82ad6549ffb47258e93b31b6e654069_LongTermDebtAdditionalNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_7661ca07-aab5-4c35-b44f-ec7761db31ee" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_5979fba3-074a-4736-8ed4-01fd6b0d39fd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7661ca07-aab5-4c35-b44f-ec7761db31ee" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_5979fba3-074a-4736-8ed4-01fd6b0d39fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_1ebf4770-5735-4010-a218-54714c47b51c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7661ca07-aab5-4c35-b44f-ec7761db31ee" xlink:to="loc_us-gaap_DerivativeNotionalAmount_1ebf4770-5735-4010-a218-54714c47b51c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeNet_0a83a011-b1b1-4e6f-aa34-1cd0cc25d57a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeFairValueOfDerivativeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7661ca07-aab5-4c35-b44f-ec7761db31ee" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeNet_0a83a011-b1b1-4e6f-aa34-1cd0cc25d57a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_957e995b-31cc-4e7a-9e89-c957e8d24a93" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7661ca07-aab5-4c35-b44f-ec7761db31ee" xlink:to="loc_us-gaap_DebtInstrumentTable_957e995b-31cc-4e7a-9e89-c957e8d24a93" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_6b2bb507-49f0-4d44-97ba-2d1cc938c155" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_957e995b-31cc-4e7a-9e89-c957e8d24a93" xlink:to="loc_us-gaap_DebtInstrumentAxis_6b2bb507-49f0-4d44-97ba-2d1cc938c155" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_6b2bb507-49f0-4d44-97ba-2d1cc938c155_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_6b2bb507-49f0-4d44-97ba-2d1cc938c155" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_6b2bb507-49f0-4d44-97ba-2d1cc938c155_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_12efabd4-2db4-4139-87e6-2c3dd4245da8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_6b2bb507-49f0-4d44-97ba-2d1cc938c155" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_12efabd4-2db4-4139-87e6-2c3dd4245da8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_CreditFacilityMember_4d62c90c-0358-467b-8acb-8337223ad043" xlink:href="bsy-20210630.xsd#bsy_CreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_12efabd4-2db4-4139-87e6-2c3dd4245da8" xlink:to="loc_bsy_CreditFacilityMember_4d62c90c-0358-467b-8acb-8337223ad043" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_a9d23385-1bed-4a89-ab15-61b4348593e9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_957e995b-31cc-4e7a-9e89-c957e8d24a93" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_a9d23385-1bed-4a89-ab15-61b4348593e9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_a9d23385-1bed-4a89-ab15-61b4348593e9_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_a9d23385-1bed-4a89-ab15-61b4348593e9" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_a9d23385-1bed-4a89-ab15-61b4348593e9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_0c367ba9-7ce4-471c-8f5a-fe061cccf7b2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_a9d23385-1bed-4a89-ab15-61b4348593e9" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_0c367ba9-7ce4-471c-8f5a-fe061cccf7b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_2acf9f5e-7fb4-42a5-b22a-c64d0c0f720d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_0c367ba9-7ce4-471c-8f5a-fe061cccf7b2" xlink:to="loc_us-gaap_LineOfCreditMember_2acf9f5e-7fb4-42a5-b22a-c64d0c0f720d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_fce5b550-fc26-403e-8ce3-858a7b09190d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_957e995b-31cc-4e7a-9e89-c957e8d24a93" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_fce5b550-fc26-403e-8ce3-858a7b09190d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_fce5b550-fc26-403e-8ce3-858a7b09190d_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_fce5b550-fc26-403e-8ce3-858a7b09190d" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_fce5b550-fc26-403e-8ce3-858a7b09190d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_485df24f-9ad3-4592-b102-05e2b38d8ff3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_fce5b550-fc26-403e-8ce3-858a7b09190d" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_485df24f-9ad3-4592-b102-05e2b38d8ff3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_668f723b-b610-435d-bfd7-45d7e7723c80" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_485df24f-9ad3-4592-b102-05e2b38d8ff3" xlink:to="loc_us-gaap_InterestRateSwapMember_668f723b-b610-435d-bfd7-45d7e7723c80" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_c86dcbfb-0567-45b8-8663-997433cdd587" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_957e995b-31cc-4e7a-9e89-c957e8d24a93" xlink:to="loc_us-gaap_HedgingDesignationAxis_c86dcbfb-0567-45b8-8663-997433cdd587" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_c86dcbfb-0567-45b8-8663-997433cdd587_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_c86dcbfb-0567-45b8-8663-997433cdd587" xlink:to="loc_us-gaap_HedgingDesignationDomain_c86dcbfb-0567-45b8-8663-997433cdd587_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_58f11e81-a256-4f77-9c63-b38470d6b1d3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_c86dcbfb-0567-45b8-8663-997433cdd587" xlink:to="loc_us-gaap_HedgingDesignationDomain_58f11e81-a256-4f77-9c63-b38470d6b1d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_bfd7d3ea-4d5b-4586-8942-40a7b9f8fd9d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_58f11e81-a256-4f77-9c63-b38470d6b1d3" xlink:to="loc_us-gaap_NondesignatedMember_bfd7d3ea-4d5b-4586-8942-40a7b9f8fd9d" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/ExecutiveBonusPlanNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#ExecutiveBonusPlanNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/ExecutiveBonusPlanNarrativeDetails" xlink:type="extended" id="i8c09fa51a63b463d8036b4bd8e058607_ExecutiveBonusPlanNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsLineItems_93dd5a5f-2b9f-4f76-b646-0c25ff7cf93d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DeferredCompensationArrangementWithIndividualManagementReportOperatingIncomeFundingThreshold_c59626aa-955c-4ef2-98cf-203d021c6c09" xlink:href="bsy-20210630.xsd#bsy_DeferredCompensationArrangementWithIndividualManagementReportOperatingIncomeFundingThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsLineItems_93dd5a5f-2b9f-4f76-b646-0c25ff7cf93d" xlink:to="loc_bsy_DeferredCompensationArrangementWithIndividualManagementReportOperatingIncomeFundingThreshold_c59626aa-955c-4ef2-98cf-203d021c6c09" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_NumberOfTradingDaysPriorToEndOfApplicableQuarterSharesDeterminedUponElectionByVolumeWeightedAveragePrice_95d30d09-6454-4ac5-a1b6-e965ab30947d" xlink:href="bsy-20210630.xsd#bsy_NumberOfTradingDaysPriorToEndOfApplicableQuarterSharesDeterminedUponElectionByVolumeWeightedAveragePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsLineItems_93dd5a5f-2b9f-4f76-b646-0c25ff7cf93d" xlink:to="loc_bsy_NumberOfTradingDaysPriorToEndOfApplicableQuarterSharesDeterminedUponElectionByVolumeWeightedAveragePrice_95d30d09-6454-4ac5-a1b6-e965ab30947d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_NumberOfTradingDaysAfterTheEndOfApplicableQuarterSharesDeterminedUponElectionByVolumeWeightedAveragePrice_d60397a2-e66c-4d6f-ada7-dbccf2b82953" xlink:href="bsy-20210630.xsd#bsy_NumberOfTradingDaysAfterTheEndOfApplicableQuarterSharesDeterminedUponElectionByVolumeWeightedAveragePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsLineItems_93dd5a5f-2b9f-4f76-b646-0c25ff7cf93d" xlink:to="loc_bsy_NumberOfTradingDaysAfterTheEndOfApplicableQuarterSharesDeterminedUponElectionByVolumeWeightedAveragePrice_d60397a2-e66c-4d6f-ada7-dbccf2b82953" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_NonDeferredIncentiveBonusThresholdForProRataAdjustment_a11b085c-a7a5-4424-ac87-d2c3b75d59c2" xlink:href="bsy-20210630.xsd#bsy_NonDeferredIncentiveBonusThresholdForProRataAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsLineItems_93dd5a5f-2b9f-4f76-b646-0c25ff7cf93d" xlink:to="loc_bsy_NonDeferredIncentiveBonusThresholdForProRataAdjustment_a11b085c-a7a5-4424-ac87-d2c3b75d59c2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense_592479b8-51e6-407b-8438-0c5e2e107896" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsLineItems_93dd5a5f-2b9f-4f76-b646-0c25ff7cf93d" xlink:to="loc_us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense_592479b8-51e6-407b-8438-0c5e2e107896" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTitleOfIndividualAndByTypeOfDeferredCompensationTable_f3be1b45-1415-4743-8dc9-3f9ea37e0db8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTitleOfIndividualAndByTypeOfDeferredCompensationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsLineItems_93dd5a5f-2b9f-4f76-b646-0c25ff7cf93d" xlink:to="loc_us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTitleOfIndividualAndByTypeOfDeferredCompensationTable_f3be1b45-1415-4743-8dc9-3f9ea37e0db8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTypeOfDeferredCompensationAxis_bafe7be2-afe0-41aa-bb5b-d85f27305407" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTypeOfDeferredCompensationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTitleOfIndividualAndByTypeOfDeferredCompensationTable_f3be1b45-1415-4743-8dc9-3f9ea37e0db8" xlink:to="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTypeOfDeferredCompensationAxis_bafe7be2-afe0-41aa-bb5b-d85f27305407" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain_bafe7be2-afe0-41aa-bb5b-d85f27305407_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTypeOfDeferredCompensationAxis_bafe7be2-afe0-41aa-bb5b-d85f27305407" xlink:to="loc_us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain_bafe7be2-afe0-41aa-bb5b-d85f27305407_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain_ad660246-5e16-4a5a-bd19-760b67f038ae" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTypeOfDeferredCompensationAxis_bafe7be2-afe0-41aa-bb5b-d85f27305407" xlink:to="loc_us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain_ad660246-5e16-4a5a-bd19-760b67f038ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationExcludingShareBasedPaymentsAndRetirementBenefitsMember_d1434f6a-c4ca-4c28-9498-fb3716855d68" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredCompensationExcludingShareBasedPaymentsAndRetirementBenefitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain_ad660246-5e16-4a5a-bd19-760b67f038ae" xlink:to="loc_us-gaap_DeferredCompensationExcludingShareBasedPaymentsAndRetirementBenefitsMember_d1434f6a-c4ca-4c28-9498-fb3716855d68" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredBonusMember_e85033a9-4b3d-4284-b34f-c24dca3a4bf7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredBonusMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationExcludingShareBasedPaymentsAndRetirementBenefitsMember_d1434f6a-c4ca-4c28-9498-fb3716855d68" xlink:to="loc_us-gaap_DeferredBonusMember_e85033a9-4b3d-4284-b34f-c24dca3a4bf7" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/RetirementPlansNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#RetirementPlansNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/RetirementPlansNarrativeDetails" xlink:type="extended" id="i18b3dd455dbb4122b11c17054269a078_RetirementPlansNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_8adfcaae-507a-485c-822c-57870054a064" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedContributionPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_e9a9e22e-6df0-4cd8-83cb-88997eae6bc5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_8adfcaae-507a-485c-822c-57870054a064" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_e9a9e22e-6df0-4cd8-83cb-88997eae6bc5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualContributionsByEmployer_5e59b768-241e-40b3-ab54-c05a616a3116" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredCompensationArrangementWithIndividualContributionsByEmployer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_8adfcaae-507a-485c-822c-57870054a064" xlink:to="loc_us-gaap_DeferredCompensationArrangementWithIndividualContributionsByEmployer_5e59b768-241e-40b3-ab54-c05a616a3116" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DividendsCommonStockStockIssuable_edda7781-75ca-47ae-a41c-ed2f804b4cd6" xlink:href="bsy-20210630.xsd#bsy_DividendsCommonStockStockIssuable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_8adfcaae-507a-485c-822c-57870054a064" xlink:to="loc_bsy_DividendsCommonStockStockIssuable_edda7781-75ca-47ae-a41c-ed2f804b4cd6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent_dd969b31-e266-4b14-8b79-11e1598adca7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_8adfcaae-507a-485c-822c-57870054a064" xlink:to="loc_us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent_dd969b31-e266-4b14-8b79-11e1598adca7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanTable_a7b04476-6836-4595-90ba-be7542d30423" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedContributionPlanTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_8adfcaae-507a-485c-822c-57870054a064" xlink:to="loc_us-gaap_DefinedContributionPlanTable_a7b04476-6836-4595-90ba-be7542d30423" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_e7879058-ce20-460a-b468-4a2ceafdb005" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedContributionPlanTable_a7b04476-6836-4595-90ba-be7542d30423" xlink:to="loc_us-gaap_VestingAxis_e7879058-ce20-460a-b468-4a2ceafdb005" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_e7879058-ce20-460a-b468-4a2ceafdb005_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_e7879058-ce20-460a-b468-4a2ceafdb005" xlink:to="loc_us-gaap_VestingDomain_e7879058-ce20-460a-b468-4a2ceafdb005_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_f1a4382e-ce79-44aa-ac2c-fe044d26cd09" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_e7879058-ce20-460a-b468-4a2ceafdb005" xlink:to="loc_us-gaap_VestingDomain_f1a4382e-ce79-44aa-ac2c-fe044d26cd09" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_106f2af5-b11a-4ef1-92be-c6665b62b8b0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_f1a4382e-ce79-44aa-ac2c-fe044d26cd09" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_106f2af5-b11a-4ef1-92be-c6665b62b8b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_89776312-7439-4bb7-a895-d4462914c54f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_f1a4382e-ce79-44aa-ac2c-fe044d26cd09" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_89776312-7439-4bb7-a895-d4462914c54f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_ddb2691a-8f5d-4cd2-8327-c98809d59579" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_f1a4382e-ce79-44aa-ac2c-fe044d26cd09" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_ddb2691a-8f5d-4cd2-8327-c98809d59579" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_ShareBasedPaymentArrangementTrancheFourMember_d629facb-d45a-4144-bf2f-86d12823b99f" xlink:href="bsy-20210630.xsd#bsy_ShareBasedPaymentArrangementTrancheFourMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_f1a4382e-ce79-44aa-ac2c-fe044d26cd09" xlink:to="loc_bsy_ShareBasedPaymentArrangementTrancheFourMember_d629facb-d45a-4144-bf2f-86d12823b99f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_ShareBasedPaymentArrangementTrancheFiveMember_f0d7af5e-2ffc-4e94-9c85-7b8961dba452" xlink:href="bsy-20210630.xsd#bsy_ShareBasedPaymentArrangementTrancheFiveMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_f1a4382e-ce79-44aa-ac2c-fe044d26cd09" xlink:to="loc_bsy_ShareBasedPaymentArrangementTrancheFiveMember_f0d7af5e-2ffc-4e94-9c85-7b8961dba452" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTaxStatusAxis_718d27d0-c5fd-44d6-ad6c-2c0d481b768a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTaxStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedContributionPlanTable_a7b04476-6836-4595-90ba-be7542d30423" xlink:to="loc_us-gaap_RetirementPlanTaxStatusAxis_718d27d0-c5fd-44d6-ad6c-2c0d481b768a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTaxStatusDomain_718d27d0-c5fd-44d6-ad6c-2c0d481b768a_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTaxStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTaxStatusAxis_718d27d0-c5fd-44d6-ad6c-2c0d481b768a" xlink:to="loc_us-gaap_RetirementPlanTaxStatusDomain_718d27d0-c5fd-44d6-ad6c-2c0d481b768a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTaxStatusDomain_1cb120e8-8808-45fe-a066-bf1d6c54b518" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTaxStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTaxStatusAxis_718d27d0-c5fd-44d6-ad6c-2c0d481b768a" xlink:to="loc_us-gaap_RetirementPlanTaxStatusDomain_1cb120e8-8808-45fe-a066-bf1d6c54b518" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonqualifiedPlanMember_dd0752d4-fc0a-4a2e-8910-bb7a4e093d3b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NonqualifiedPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTaxStatusDomain_1cb120e8-8808-45fe-a066-bf1d6c54b518" xlink:to="loc_us-gaap_NonqualifiedPlanMember_dd0752d4-fc0a-4a2e-8910-bb7a4e093d3b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis_4f1d22a6-7683-4c7f-87b8-77062b182447" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedContributionPlanTable_a7b04476-6836-4595-90ba-be7542d30423" xlink:to="loc_us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis_4f1d22a6-7683-4c7f-87b8-77062b182447" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain_4f1d22a6-7683-4c7f-87b8-77062b182447_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis_4f1d22a6-7683-4c7f-87b8-77062b182447" xlink:to="loc_us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain_4f1d22a6-7683-4c7f-87b8-77062b182447_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain_c31bcfdf-c687-4ce3-af9d-8b1fab8a9be2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis_4f1d22a6-7683-4c7f-87b8-77062b182447" xlink:to="loc_us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain_c31bcfdf-c687-4ce3-af9d-8b1fab8a9be2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualByTypeOfCompensationPensionAndOtherPostretirementBenefitsMember_efe7416e-8366-4567-8bb3-382ffac3ef4c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredCompensationArrangementWithIndividualByTypeOfCompensationPensionAndOtherPostretirementBenefitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain_c31bcfdf-c687-4ce3-af9d-8b1fab8a9be2" xlink:to="loc_us-gaap_DeferredCompensationArrangementWithIndividualByTypeOfCompensationPensionAndOtherPostretirementBenefitsMember_efe7416e-8366-4567-8bb3-382ffac3ef4c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardDateAxis_76104450-7dc9-490a-a5f0-d5d1de441aa5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AwardDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedContributionPlanTable_a7b04476-6836-4595-90ba-be7542d30423" xlink:to="loc_us-gaap_AwardDateAxis_76104450-7dc9-490a-a5f0-d5d1de441aa5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardDateDomain_76104450-7dc9-490a-a5f0-d5d1de441aa5_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AwardDateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardDateAxis_76104450-7dc9-490a-a5f0-d5d1de441aa5" xlink:to="loc_us-gaap_AwardDateDomain_76104450-7dc9-490a-a5f0-d5d1de441aa5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardDateDomain_d23ca962-9344-421a-a7a9-498d4f910670" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AwardDateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardDateAxis_76104450-7dc9-490a-a5f0-d5d1de441aa5" xlink:to="loc_us-gaap_AwardDateDomain_d23ca962-9344-421a-a7a9-498d4f910670" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_PriorToJanuary2016AwardsMember_44b5bc13-8eb9-4268-a7a7-8e6bca60cc54" xlink:href="bsy-20210630.xsd#bsy_PriorToJanuary2016AwardsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AwardDateDomain_d23ca962-9344-421a-a7a9-498d4f910670" xlink:to="loc_bsy_PriorToJanuary2016AwardsMember_44b5bc13-8eb9-4268-a7a7-8e6bca60cc54" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_AfterJanuary2016AwardsMember_411b1b27-777a-42c8-a526-2df34c709164" xlink:href="bsy-20210630.xsd#bsy_AfterJanuary2016AwardsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AwardDateDomain_d23ca962-9344-421a-a7a9-498d4f910670" xlink:to="loc_bsy_AfterJanuary2016AwardsMember_411b1b27-777a-42c8-a526-2df34c709164" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/CommonStockSalesRepurchasesandIssuancesofCompanyCapitalStockNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#CommonStockSalesRepurchasesandIssuancesofCompanyCapitalStockNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/CommonStockSalesRepurchasesandIssuancesofCompanyCapitalStockNarrativeDetails" xlink:type="extended" id="i5f5e0e299373471fb8cb7e72eb6c4085_CommonStockSalesRepurchasesandIssuancesofCompanyCapitalStockNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_70c7a48f-d818-401d-9971-2268fa0750c8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_33a80d24-155d-476a-a80b-699ba7a48d62" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_70c7a48f-d818-401d-9971-2268fa0750c8" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_33a80d24-155d-476a-a80b-699ba7a48d62" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_CommonStockPurchaseAgreementAmountAuthorized_80820ff8-b094-431b-96ce-784e79fd16c8" xlink:href="bsy-20210630.xsd#bsy_CommonStockPurchaseAgreementAmountAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_70c7a48f-d818-401d-9971-2268fa0750c8" xlink:to="loc_bsy_CommonStockPurchaseAgreementAmountAuthorized_80820ff8-b094-431b-96ce-784e79fd16c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_3591ad1b-8e3b-4fc7-a092-eb8476deebf3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_70c7a48f-d818-401d-9971-2268fa0750c8" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_3591ad1b-8e3b-4fc7-a092-eb8476deebf3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_410879d2-d00d-4a95-8157-5755d0508a6f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_70c7a48f-d818-401d-9971-2268fa0750c8" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_410879d2-d00d-4a95-8157-5755d0508a6f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodNetOfSharesWithheld_56937d73-f0af-4e8d-b5c1-e85e0f27dffe" xlink:href="bsy-20210630.xsd#bsy_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodNetOfSharesWithheld"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_70c7a48f-d818-401d-9971-2268fa0750c8" xlink:to="loc_bsy_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodNetOfSharesWithheld_56937d73-f0af-4e8d-b5c1-e85e0f27dffe" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_ShareBasedPaymentArrangementSharesWithheldForCostOfOptionsAndTaxWithholdingObligation_fde5ec3f-8cf5-4237-b346-10d8468448d0" xlink:href="bsy-20210630.xsd#bsy_ShareBasedPaymentArrangementSharesWithheldForCostOfOptionsAndTaxWithholdingObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_70c7a48f-d818-401d-9971-2268fa0750c8" xlink:to="loc_bsy_ShareBasedPaymentArrangementSharesWithheldForCostOfOptionsAndTaxWithholdingObligation_fde5ec3f-8cf5-4237-b346-10d8468448d0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_bcefb974-d9b5-4700-a5e4-12dac9e1a19c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_70c7a48f-d818-401d-9971-2268fa0750c8" xlink:to="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_bcefb974-d9b5-4700-a5e4-12dac9e1a19c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationCashFlowEffectCashUsedToSettleAwards_80bd32a7-fc57-413c-9312-0693c539e83a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationCashFlowEffectCashUsedToSettleAwards"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_70c7a48f-d818-401d-9971-2268fa0750c8" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationCashFlowEffectCashUsedToSettleAwards_80bd32a7-fc57-413c-9312-0693c539e83a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_ShareBasedPaymentArrangementSharesRepurchasedByCompanyAfterExerciseValue_3e6a8587-b82b-419d-959f-9054459a6f46" xlink:href="bsy-20210630.xsd#bsy_ShareBasedPaymentArrangementSharesRepurchasedByCompanyAfterExerciseValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_70c7a48f-d818-401d-9971-2268fa0750c8" xlink:to="loc_bsy_ShareBasedPaymentArrangementSharesRepurchasedByCompanyAfterExerciseValue_3e6a8587-b82b-419d-959f-9054459a6f46" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_ShareBasedPaymentArrangementSharesRepurchasedByCompanyAfterExerciseShares_b8a9e6e9-9d57-45fe-8c04-817e00639914" xlink:href="bsy-20210630.xsd#bsy_ShareBasedPaymentArrangementSharesRepurchasedByCompanyAfterExerciseShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_70c7a48f-d818-401d-9971-2268fa0750c8" xlink:to="loc_bsy_ShareBasedPaymentArrangementSharesRepurchasedByCompanyAfterExerciseShares_b8a9e6e9-9d57-45fe-8c04-817e00639914" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_86f5bad3-6567-4417-bf21-11df3b09859e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_70c7a48f-d818-401d-9971-2268fa0750c8" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_86f5bad3-6567-4417-bf21-11df3b09859e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualSharesIssued_be5e8d64-7fee-4749-a004-e8af31779ba1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredCompensationArrangementWithIndividualSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_70c7a48f-d818-401d-9971-2268fa0750c8" xlink:to="loc_us-gaap_DeferredCompensationArrangementWithIndividualSharesIssued_be5e8d64-7fee-4749-a004-e8af31779ba1" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DeferredCompensationArrangementWithIndividualSharesIssuedGross_385f581a-4e82-46fd-9ec1-d1fb64599a46" xlink:href="bsy-20210630.xsd#bsy_DeferredCompensationArrangementWithIndividualSharesIssuedGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_70c7a48f-d818-401d-9971-2268fa0750c8" xlink:to="loc_bsy_DeferredCompensationArrangementWithIndividualSharesIssuedGross_385f581a-4e82-46fd-9ec1-d1fb64599a46" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_45036d31-cba9-4f91-8a84-77116b815dfb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_70c7a48f-d818-401d-9971-2268fa0750c8" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_45036d31-cba9-4f91-8a84-77116b815dfb" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_4afe08ce-3fd5-46be-9f32-113f83448f4f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_70c7a48f-d818-401d-9971-2268fa0750c8" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_4afe08ce-3fd5-46be-9f32-113f83448f4f" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_5bf31316-dfe5-418c-ac4e-2fcec1589e93" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_70c7a48f-d818-401d-9971-2268fa0750c8" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_5bf31316-dfe5-418c-ac4e-2fcec1589e93" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_38bb0fe8-18f8-45c3-bf13-c942100a090c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_5bf31316-dfe5-418c-ac4e-2fcec1589e93" xlink:to="loc_us-gaap_StatementClassOfStockAxis_38bb0fe8-18f8-45c3-bf13-c942100a090c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_38bb0fe8-18f8-45c3-bf13-c942100a090c_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_38bb0fe8-18f8-45c3-bf13-c942100a090c" xlink:to="loc_us-gaap_ClassOfStockDomain_38bb0fe8-18f8-45c3-bf13-c942100a090c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_23b2a3bf-bb8b-4555-b582-174f3e0e372d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_38bb0fe8-18f8-45c3-bf13-c942100a090c" xlink:to="loc_us-gaap_ClassOfStockDomain_23b2a3bf-bb8b-4555-b582-174f3e0e372d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_b7746bd3-ef3d-457a-b3a5-23a95554107c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_23b2a3bf-bb8b-4555-b582-174f3e0e372d" xlink:to="loc_us-gaap_CommonClassBMember_b7746bd3-ef3d-457a-b3a5-23a95554107c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_baf56d9c-efd8-468b-b548-55981dd74e2b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_5bf31316-dfe5-418c-ac4e-2fcec1589e93" xlink:to="loc_us-gaap_AwardTypeAxis_baf56d9c-efd8-468b-b548-55981dd74e2b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_baf56d9c-efd8-468b-b548-55981dd74e2b_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_baf56d9c-efd8-468b-b548-55981dd74e2b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_baf56d9c-efd8-468b-b548-55981dd74e2b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_17dbdc7f-27b8-4098-b82a-bffd70af2a27" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_baf56d9c-efd8-468b-b548-55981dd74e2b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_17dbdc7f-27b8-4098-b82a-bffd70af2a27" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_7ed7218c-26f6-41fb-bf27-f7997c55f3e0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_17dbdc7f-27b8-4098-b82a-bffd70af2a27" xlink:to="loc_us-gaap_EmployeeStockOptionMember_7ed7218c-26f6-41fb-bf27-f7997c55f3e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_PerformanceBasedRestrictedStockUnitsRSUsTwoThousandSixteenMember_450433b4-8f52-4d6c-b22a-4995adabac03" xlink:href="bsy-20210630.xsd#bsy_PerformanceBasedRestrictedStockUnitsRSUsTwoThousandSixteenMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_17dbdc7f-27b8-4098-b82a-bffd70af2a27" xlink:to="loc_bsy_PerformanceBasedRestrictedStockUnitsRSUsTwoThousandSixteenMember_450433b4-8f52-4d6c-b22a-4995adabac03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_a7d022c7-7e96-4307-8b94-71d21eff4324" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_5bf31316-dfe5-418c-ac4e-2fcec1589e93" xlink:to="loc_us-gaap_PlanNameAxis_a7d022c7-7e96-4307-8b94-71d21eff4324" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_a7d022c7-7e96-4307-8b94-71d21eff4324_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_a7d022c7-7e96-4307-8b94-71d21eff4324" xlink:to="loc_us-gaap_PlanNameDomain_a7d022c7-7e96-4307-8b94-71d21eff4324_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_75f7140c-51ea-4fe8-b770-05c33aee97e5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_a7d022c7-7e96-4307-8b94-71d21eff4324" xlink:to="loc_us-gaap_PlanNameDomain_75f7140c-51ea-4fe8-b770-05c33aee97e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_EquityIncentivePlanMember_d32fca2d-5664-4be7-a5af-81b381ccc9c5" xlink:href="bsy-20210630.xsd#bsy_EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_75f7140c-51ea-4fe8-b770-05c33aee97e5" xlink:to="loc_bsy_EquityIncentivePlanMember_d32fca2d-5664-4be7-a5af-81b381ccc9c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_BonusPlanIncentiveMember_64aee08e-7b28-4924-aefc-7c45cdf7ed92" xlink:href="bsy-20210630.xsd#bsy_BonusPlanIncentiveMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_75f7140c-51ea-4fe8-b770-05c33aee97e5" xlink:to="loc_bsy_BonusPlanIncentiveMember_64aee08e-7b28-4924-aefc-7c45cdf7ed92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_16e40e73-09a2-4296-a04b-427ed027b2b7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_5bf31316-dfe5-418c-ac4e-2fcec1589e93" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_16e40e73-09a2-4296-a04b-427ed027b2b7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_16e40e73-09a2-4296-a04b-427ed027b2b7_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_16e40e73-09a2-4296-a04b-427ed027b2b7" xlink:to="loc_us-gaap_EquityComponentDomain_16e40e73-09a2-4296-a04b-427ed027b2b7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_92b6b07f-6ce2-40f7-8130-b7596c739a5c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_16e40e73-09a2-4296-a04b-427ed027b2b7" xlink:to="loc_us-gaap_EquityComponentDomain_92b6b07f-6ce2-40f7-8130-b7596c739a5c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_80582da4-6627-4eeb-b0ad-5fa62992cdc3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_92b6b07f-6ce2-40f7-8130-b7596c739a5c" xlink:to="loc_us-gaap_CommonStockMember_80582da4-6627-4eeb-b0ad-5fa62992cdc3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationShareBasedPaymentsMember_fccaf16a-7f85-4c7e-b95f-fc13cb939298" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredCompensationShareBasedPaymentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_92b6b07f-6ce2-40f7-8130-b7596c739a5c" xlink:to="loc_us-gaap_DeferredCompensationShareBasedPaymentsMember_fccaf16a-7f85-4c7e-b95f-fc13cb939298" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis_c508fb3f-ae6f-4d17-84eb-7dd87a38ca67" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_5bf31316-dfe5-418c-ac4e-2fcec1589e93" xlink:to="loc_us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis_c508fb3f-ae6f-4d17-84eb-7dd87a38ca67" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain_c508fb3f-ae6f-4d17-84eb-7dd87a38ca67_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis_c508fb3f-ae6f-4d17-84eb-7dd87a38ca67" xlink:to="loc_us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain_c508fb3f-ae6f-4d17-84eb-7dd87a38ca67_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain_44a42247-ccfe-4ee4-841a-e4ad2836e562" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis_c508fb3f-ae6f-4d17-84eb-7dd87a38ca67" xlink:to="loc_us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain_44a42247-ccfe-4ee4-841a-e4ad2836e562" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualByTypeOfCompensationPensionAndOtherPostretirementBenefitsMember_8a5689ec-e3dd-43f8-bd4c-93c967752e21" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredCompensationArrangementWithIndividualByTypeOfCompensationPensionAndOtherPostretirementBenefitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherPostretirementBenefitsIndividualContractsTypeOfDeferredCompensationDomain_44a42247-ccfe-4ee4-841a-e4ad2836e562" xlink:to="loc_us-gaap_DeferredCompensationArrangementWithIndividualByTypeOfCompensationPensionAndOtherPostretirementBenefitsMember_8a5689ec-e3dd-43f8-bd4c-93c967752e21" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTypeOfDeferredCompensationAxis_060a6825-9d7f-42d2-ad82-2e5d2fd0fce3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTypeOfDeferredCompensationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_5bf31316-dfe5-418c-ac4e-2fcec1589e93" xlink:to="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTypeOfDeferredCompensationAxis_060a6825-9d7f-42d2-ad82-2e5d2fd0fce3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain_060a6825-9d7f-42d2-ad82-2e5d2fd0fce3_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTypeOfDeferredCompensationAxis_060a6825-9d7f-42d2-ad82-2e5d2fd0fce3" xlink:to="loc_us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain_060a6825-9d7f-42d2-ad82-2e5d2fd0fce3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain_6cb65cbb-6461-4f9d-8482-f2516fa1c1f4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualExcludingShareBasedPaymentsAndPostretirementBenefitsByTypeOfDeferredCompensationAxis_060a6825-9d7f-42d2-ad82-2e5d2fd0fce3" xlink:to="loc_us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain_6cb65cbb-6461-4f9d-8482-f2516fa1c1f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredProfitSharingMember_b137148f-fb1a-4ee4-b42e-b7112948f187" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredProfitSharingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredBonusAndProfitSharingArrangementIndividualContractTypeOfDeferredCompensationDomain_6cb65cbb-6461-4f9d-8482-f2516fa1c1f4" xlink:to="loc_us-gaap_DeferredProfitSharingMember_b137148f-fb1a-4ee4-b42e-b7112948f187" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_b896f8c5-02f6-4db2-beb9-01d9d46b8ee0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_5bf31316-dfe5-418c-ac4e-2fcec1589e93" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_b896f8c5-02f6-4db2-beb9-01d9d46b8ee0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b896f8c5-02f6-4db2-beb9-01d9d46b8ee0_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_b896f8c5-02f6-4db2-beb9-01d9d46b8ee0" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b896f8c5-02f6-4db2-beb9-01d9d46b8ee0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_908a45f7-cac5-480c-b683-73b185863b29" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_b896f8c5-02f6-4db2-beb9-01d9d46b8ee0" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_908a45f7-cac5-480c-b683-73b185863b29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_SeequentMember_ad2a7135-210d-4a37-af6e-49960e93c6b5" xlink:href="bsy-20210630.xsd#bsy_SeequentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_908a45f7-cac5-480c-b683-73b185863b29" xlink:to="loc_bsy_SeequentMember_ad2a7135-210d-4a37-af6e-49960e93c6b5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_5fbd85e8-56b9-491c-9450-1e65c48a5e8a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_5bf31316-dfe5-418c-ac4e-2fcec1589e93" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_5fbd85e8-56b9-491c-9450-1e65c48a5e8a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_5fbd85e8-56b9-491c-9450-1e65c48a5e8a_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_5fbd85e8-56b9-491c-9450-1e65c48a5e8a" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_5fbd85e8-56b9-491c-9450-1e65c48a5e8a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_8ce0c130-1b32-44fe-bfaf-53420ec64f45" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_5fbd85e8-56b9-491c-9450-1e65c48a5e8a" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_8ce0c130-1b32-44fe-bfaf-53420ec64f45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrivatePlacementMember_16995375-baa5-4611-b80d-0bdb4227808f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PrivatePlacementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_8ce0c130-1b32-44fe-bfaf-53420ec64f45" xlink:to="loc_us-gaap_PrivatePlacementMember_16995375-baa5-4611-b80d-0bdb4227808f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_PrivatePlacementDirectInvestorInvestmentMember_8398d1c8-1826-406f-a0ad-6ec2f067ee36" xlink:href="bsy-20210630.xsd#bsy_PrivatePlacementDirectInvestorInvestmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_8ce0c130-1b32-44fe-bfaf-53420ec64f45" xlink:to="loc_bsy_PrivatePlacementDirectInvestorInvestmentMember_8398d1c8-1826-406f-a0ad-6ec2f067ee36" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/CommonStockGlobalEmployeeStockPurchasePlanDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#CommonStockGlobalEmployeeStockPurchasePlanDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/CommonStockGlobalEmployeeStockPurchasePlanDetails" xlink:type="extended" id="i45efb7724a714a09baf5769d3ca4daf4_CommonStockGlobalEmployeeStockPurchasePlanDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_c5622162-6c05-424b-86a8-91f24fbbf586" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate_d069d8f3-1731-4fd7-90e5-0c6291f386b2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_c5622162-6c05-424b-86a8-91f24fbbf586" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate_d069d8f3-1731-4fd7-90e5-0c6291f386b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeAnnualContributionAmount_129c512a-c4e7-4838-a65e-2023d60e2695" xlink:href="bsy-20210630.xsd#bsy_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeAnnualContributionAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_c5622162-6c05-424b-86a8-91f24fbbf586" xlink:to="loc_bsy_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeAnnualContributionAmount_129c512a-c4e7-4838-a65e-2023d60e2695" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_a6004469-2faa-4324-99ca-215a22383314" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_c5622162-6c05-424b-86a8-91f24fbbf586" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_a6004469-2faa-4324-99ca-215a22383314" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_4d58ef99-d205-45ef-ba5f-8f5cbbd97d69" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_c5622162-6c05-424b-86a8-91f24fbbf586" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_4d58ef99-d205-45ef-ba5f-8f5cbbd97d69" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherEmployeeRelatedLiabilitiesCurrent_ed70d9f3-02fe-45e7-9d2b-27a8553d76d5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherEmployeeRelatedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_c5622162-6c05-424b-86a8-91f24fbbf586" xlink:to="loc_us-gaap_OtherEmployeeRelatedLiabilitiesCurrent_ed70d9f3-02fe-45e7-9d2b-27a8553d76d5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_34868e63-5a4c-4ee4-a404-8a8c6350fa50" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_c5622162-6c05-424b-86a8-91f24fbbf586" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_34868e63-5a4c-4ee4-a404-8a8c6350fa50" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_1ac09b6e-5478-4570-a4c7-73bed487c3f3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_34868e63-5a4c-4ee4-a404-8a8c6350fa50" xlink:to="loc_us-gaap_StatementClassOfStockAxis_1ac09b6e-5478-4570-a4c7-73bed487c3f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_1ac09b6e-5478-4570-a4c7-73bed487c3f3_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_1ac09b6e-5478-4570-a4c7-73bed487c3f3" xlink:to="loc_us-gaap_ClassOfStockDomain_1ac09b6e-5478-4570-a4c7-73bed487c3f3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_2d1f483e-b6f2-49c3-9bbc-cbfb0a02e7cc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_1ac09b6e-5478-4570-a4c7-73bed487c3f3" xlink:to="loc_us-gaap_ClassOfStockDomain_2d1f483e-b6f2-49c3-9bbc-cbfb0a02e7cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_1dce87d7-e630-4294-b621-7bf1e480e47d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_2d1f483e-b6f2-49c3-9bbc-cbfb0a02e7cc" xlink:to="loc_us-gaap_CommonClassBMember_1dce87d7-e630-4294-b621-7bf1e480e47d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_9a1aba47-3159-4e37-844f-30843eebb12c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_34868e63-5a4c-4ee4-a404-8a8c6350fa50" xlink:to="loc_us-gaap_AwardTypeAxis_9a1aba47-3159-4e37-844f-30843eebb12c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9a1aba47-3159-4e37-844f-30843eebb12c_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_9a1aba47-3159-4e37-844f-30843eebb12c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9a1aba47-3159-4e37-844f-30843eebb12c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_40c7e69f-de08-475f-9aeb-f59213e5736f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_9a1aba47-3159-4e37-844f-30843eebb12c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_40c7e69f-de08-475f-9aeb-f59213e5736f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_ed38d5ca-8719-4495-ba8e-6cc2ca49b37e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_40c7e69f-de08-475f-9aeb-f59213e5736f" xlink:to="loc_us-gaap_EmployeeStockMember_ed38d5ca-8719-4495-ba8e-6cc2ca49b37e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/AccumulatedOtherComprehensiveLossRollforwardofAOCIDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#AccumulatedOtherComprehensiveLossRollforwardofAOCIDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/AccumulatedOtherComprehensiveLossRollforwardofAOCIDetails" xlink:type="extended" id="i52844bc854d646ebae783071a5d9c853_AccumulatedOtherComprehensiveLossRollforwardofAOCIDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_2bf990f2-3ec0-4e1b-9846-9b53ec98886c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_fd3c7535-da9f-4099-aac1-89bf7ab5681f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_2bf990f2-3ec0-4e1b-9846-9b53ec98886c" xlink:to="loc_us-gaap_StockholdersEquity_fd3c7535-da9f-4099-aac1-89bf7ab5681f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent_3a14699c-21ea-4deb-b077-39ac185f3236" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_2bf990f2-3ec0-4e1b-9846-9b53ec98886c" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent_3a14699c-21ea-4deb-b077-39ac185f3236" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1_abdc7a58-d5e3-444e-a373-4a1925d60fc1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_2bf990f2-3ec0-4e1b-9846-9b53ec98886c" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1_abdc7a58-d5e3-444e-a373-4a1925d60fc1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_7a81300b-f4eb-479d-a217-a9150f1550ae" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_2bf990f2-3ec0-4e1b-9846-9b53ec98886c" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_7a81300b-f4eb-479d-a217-a9150f1550ae" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_d3858945-8935-49ea-83aa-12f7f629cb04" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_abc6936b-4f02-42fc-b80b-781cef102d73" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_2bf990f2-3ec0-4e1b-9846-9b53ec98886c" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_abc6936b-4f02-42fc-b80b-781cef102d73" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_93942b11-0743-4b86-a384-e3e950906fcd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_abc6936b-4f02-42fc-b80b-781cef102d73" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_93942b11-0743-4b86-a384-e3e950906fcd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_93942b11-0743-4b86-a384-e3e950906fcd_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_93942b11-0743-4b86-a384-e3e950906fcd" xlink:to="loc_us-gaap_EquityComponentDomain_93942b11-0743-4b86-a384-e3e950906fcd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_7325664a-46b7-44cd-8c1c-2bd40a19b728" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_93942b11-0743-4b86-a384-e3e950906fcd" xlink:to="loc_us-gaap_EquityComponentDomain_7325664a-46b7-44cd-8c1c-2bd40a19b728" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_cfdf06ae-eee2-4fc6-8a1e-4ae47815f128" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_7325664a-46b7-44cd-8c1c-2bd40a19b728" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_cfdf06ae-eee2-4fc6-8a1e-4ae47815f128" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLossMember_fec8aa6f-6044-4322-8a12-cebc606b20ff" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_7325664a-46b7-44cd-8c1c-2bd40a19b728" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLossMember_fec8aa6f-6044-4322-8a12-cebc606b20ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_e512345f-c2e0-4245-87ef-f57e79b70f59" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_7325664a-46b7-44cd-8c1c-2bd40a19b728" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_e512345f-c2e0-4245-87ef-f57e79b70f59" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/EquityAwardsandInstrumentsSummaryofStockBasedCompensationExpenseDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#EquityAwardsandInstrumentsSummaryofStockBasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/EquityAwardsandInstrumentsSummaryofStockBasedCompensationExpenseDetails" xlink:type="extended" id="ic2d1c8196f0f43c5b67ec2322ea238b9_EquityAwardsandInstrumentsSummaryofStockBasedCompensationExpenseDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_8ff0b0d4-ec85-4aa3-a519-a8addf37544b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_f11aaa2b-6b20-470b-adea-f97cfb773d81" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_8ff0b0d4-ec85-4aa3-a519-a8addf37544b" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_f11aaa2b-6b20-470b-adea-f97cfb773d81" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_ShareBasedPaymentArrangementExpenseAccrued_9cc71c6f-a7c9-4707-809b-8da495f7f0da" xlink:href="bsy-20210630.xsd#bsy_ShareBasedPaymentArrangementExpenseAccrued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_8ff0b0d4-ec85-4aa3-a519-a8addf37544b" xlink:to="loc_bsy_ShareBasedPaymentArrangementExpenseAccrued_9cc71c6f-a7c9-4707-809b-8da495f7f0da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_458914f5-d891-43e5-93f8-ef75e9cfbec3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_8ff0b0d4-ec85-4aa3-a519-a8addf37544b" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_458914f5-d891-43e5-93f8-ef75e9cfbec3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_9c36b304-1229-48d7-b265-d8109c580864" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_458914f5-d891-43e5-93f8-ef75e9cfbec3" xlink:to="loc_us-gaap_AwardTypeAxis_9c36b304-1229-48d7-b265-d8109c580864" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9c36b304-1229-48d7-b265-d8109c580864_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_9c36b304-1229-48d7-b265-d8109c580864" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9c36b304-1229-48d7-b265-d8109c580864_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9fa50528-61de-4d3e-802d-321afccf5582" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_9c36b304-1229-48d7-b265-d8109c580864" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9fa50528-61de-4d3e-802d-321afccf5582" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_9789fc48-0d71-4ce8-af0b-c3f2ef264034" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9fa50528-61de-4d3e-802d-321afccf5582" xlink:to="loc_us-gaap_EmployeeStockOptionMember_9789fc48-0d71-4ce8-af0b-c3f2ef264034" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_RestrictedStockAndRestrictedStockUnitsRSUsMember_a8d16fa5-4f1b-4ad8-8c14-286a3aa3ebaa" xlink:href="bsy-20210630.xsd#bsy_RestrictedStockAndRestrictedStockUnitsRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9fa50528-61de-4d3e-802d-321afccf5582" xlink:to="loc_bsy_RestrictedStockAndRestrictedStockUnitsRSUsMember_a8d16fa5-4f1b-4ad8-8c14-286a3aa3ebaa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_StockGrantMember_b922b8e5-20da-4862-8b91-98dfbe492360" xlink:href="bsy-20210630.xsd#bsy_StockGrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9fa50528-61de-4d3e-802d-321afccf5582" xlink:to="loc_bsy_StockGrantMember_b922b8e5-20da-4862-8b91-98dfbe492360" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_BonusPlanMember_dcc6596a-0c19-4c43-86f1-24d17f542a60" xlink:href="bsy-20210630.xsd#bsy_BonusPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9fa50528-61de-4d3e-802d-321afccf5582" xlink:to="loc_bsy_BonusPlanMember_dcc6596a-0c19-4c43-86f1-24d17f542a60" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_BentleySystemsIncorporatedGlobalEmployeeStockPurchasePlanMember_dfdbfd81-a9a8-4eae-b659-c3a77ae32360" xlink:href="bsy-20210630.xsd#bsy_BentleySystemsIncorporatedGlobalEmployeeStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9fa50528-61de-4d3e-802d-321afccf5582" xlink:to="loc_bsy_BentleySystemsIncorporatedGlobalEmployeeStockPurchasePlanMember_dfdbfd81-a9a8-4eae-b659-c3a77ae32360" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_0333f974-7e6e-4113-a0a2-e00b73ed2dca" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_458914f5-d891-43e5-93f8-ef75e9cfbec3" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_0333f974-7e6e-4113-a0a2-e00b73ed2dca" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_0333f974-7e6e-4113-a0a2-e00b73ed2dca_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_0333f974-7e6e-4113-a0a2-e00b73ed2dca" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_0333f974-7e6e-4113-a0a2-e00b73ed2dca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_c3ea1c20-1196-48b0-9f7a-19be995cb1a4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_0333f974-7e6e-4113-a0a2-e00b73ed2dca" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_c3ea1c20-1196-48b0-9f7a-19be995cb1a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_3ab5c137-9632-4333-ad57-602ce34ed28a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_c3ea1c20-1196-48b0-9f7a-19be995cb1a4" xlink:to="loc_us-gaap_CostOfSalesMember_3ab5c137-9632-4333-ad57-602ce34ed28a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_da21a26b-5075-419d-a06a-5707cff06824" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_c3ea1c20-1196-48b0-9f7a-19be995cb1a4" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_da21a26b-5075-419d-a06a-5707cff06824" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpenseMember_988c8336-d6b5-4d2e-8d50-5e46080dbee6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SellingAndMarketingExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_c3ea1c20-1196-48b0-9f7a-19be995cb1a4" xlink:to="loc_us-gaap_SellingAndMarketingExpenseMember_988c8336-d6b5-4d2e-8d50-5e46080dbee6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_6d351d2a-2b6d-44b5-af38-8808d100fb8f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_c3ea1c20-1196-48b0-9f7a-19be995cb1a4" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_6d351d2a-2b6d-44b5-af38-8808d100fb8f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_3cd6fd0f-fd96-48af-8cf8-b41cd94dc2c6" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_458914f5-d891-43e5-93f8-ef75e9cfbec3" xlink:to="loc_srt_ProductOrServiceAxis_3cd6fd0f-fd96-48af-8cf8-b41cd94dc2c6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_3cd6fd0f-fd96-48af-8cf8-b41cd94dc2c6_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_3cd6fd0f-fd96-48af-8cf8-b41cd94dc2c6" xlink:to="loc_srt_ProductsAndServicesDomain_3cd6fd0f-fd96-48af-8cf8-b41cd94dc2c6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_b9dfb74f-6493-4650-9c78-887fd6973253" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_3cd6fd0f-fd96-48af-8cf8-b41cd94dc2c6" xlink:to="loc_srt_ProductsAndServicesDomain_b9dfb74f-6493-4650-9c78-887fd6973253" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_SubscriptionsAndLicensesMember_6c4bf896-6d46-4abb-adb6-31d146d6ab23" xlink:href="bsy-20210630.xsd#bsy_SubscriptionsAndLicensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_b9dfb74f-6493-4650-9c78-887fd6973253" xlink:to="loc_bsy_SubscriptionsAndLicensesMember_6c4bf896-6d46-4abb-adb6-31d146d6ab23" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/EquityAwardsandInstrumentsOptionsOutstandingRollforwardDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#EquityAwardsandInstrumentsOptionsOutstandingRollforwardDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/EquityAwardsandInstrumentsOptionsOutstandingRollforwardDetails" xlink:type="extended" id="i28c21ea4bb7f4d669739c20ed482068c_EquityAwardsandInstrumentsOptionsOutstandingRollforwardDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8c6900fe-56a6-4ca6-86c7-a58a2e2bec46" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_9651b9f9-0eb2-417b-8f0b-67898bd8b299" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8c6900fe-56a6-4ca6-86c7-a58a2e2bec46" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_9651b9f9-0eb2-417b-8f0b-67898bd8b299" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_e01e258b-7590-43eb-b6c0-dc8384107d70" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_9651b9f9-0eb2-417b-8f0b-67898bd8b299" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_e01e258b-7590-43eb-b6c0-dc8384107d70" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_7aeaa2eb-e6f6-4835-b8e7-56f4873027fb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_9651b9f9-0eb2-417b-8f0b-67898bd8b299" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_7aeaa2eb-e6f6-4835-b8e7-56f4873027fb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_524d3a4e-14e4-438d-87d7-e1b44abedc23" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_9651b9f9-0eb2-417b-8f0b-67898bd8b299" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_524d3a4e-14e4-438d-87d7-e1b44abedc23" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_7f5ae60c-5ee9-4ba4-a481-1afb6bbb30be" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_b4ac2c37-2641-4616-86e8-7bdc9783d1b2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8c6900fe-56a6-4ca6-86c7-a58a2e2bec46" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_b4ac2c37-2641-4616-86e8-7bdc9783d1b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_ShareBasedPaymentArrangementByShareBasedPaymentAwardOptionsWeightedAverageExercisePricePerShareRollForward_21403015-efd3-4782-9fd5-3c95b0f3a024" xlink:href="bsy-20210630.xsd#bsy_ShareBasedPaymentArrangementByShareBasedPaymentAwardOptionsWeightedAverageExercisePricePerShareRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8c6900fe-56a6-4ca6-86c7-a58a2e2bec46" xlink:to="loc_bsy_ShareBasedPaymentArrangementByShareBasedPaymentAwardOptionsWeightedAverageExercisePricePerShareRollForward_21403015-efd3-4782-9fd5-3c95b0f3a024" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_95288129-a678-4740-86cc-a468846ad945" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_ShareBasedPaymentArrangementByShareBasedPaymentAwardOptionsWeightedAverageExercisePricePerShareRollForward_21403015-efd3-4782-9fd5-3c95b0f3a024" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_95288129-a678-4740-86cc-a468846ad945" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_ce34c08d-35ec-455a-814d-e8daa519e819" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_ShareBasedPaymentArrangementByShareBasedPaymentAwardOptionsWeightedAverageExercisePricePerShareRollForward_21403015-efd3-4782-9fd5-3c95b0f3a024" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_ce34c08d-35ec-455a-814d-e8daa519e819" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_62fbc251-691c-40be-ab1b-5c708039d93c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_ShareBasedPaymentArrangementByShareBasedPaymentAwardOptionsWeightedAverageExercisePricePerShareRollForward_21403015-efd3-4782-9fd5-3c95b0f3a024" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_62fbc251-691c-40be-ab1b-5c708039d93c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_ab089f3d-ba27-45f7-9cb1-71dad77b77fc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_aa925c59-6abc-474c-a1a1-82f0b6b8318c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8c6900fe-56a6-4ca6-86c7-a58a2e2bec46" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_aa925c59-6abc-474c-a1a1-82f0b6b8318c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_52195186-dd1b-4cd5-a595-8d2c7eb066cb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8c6900fe-56a6-4ca6-86c7-a58a2e2bec46" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_52195186-dd1b-4cd5-a595-8d2c7eb066cb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_0b26104b-ffd2-4118-9ac0-8824b895814a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8c6900fe-56a6-4ca6-86c7-a58a2e2bec46" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_0b26104b-ffd2-4118-9ac0-8824b895814a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_8a8b8d44-78b8-4b7d-8961-d02564b1b9e5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8c6900fe-56a6-4ca6-86c7-a58a2e2bec46" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_8a8b8d44-78b8-4b7d-8961-d02564b1b9e5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_29d69098-7aba-4c33-8bed-09b394e935a5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8c6900fe-56a6-4ca6-86c7-a58a2e2bec46" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_29d69098-7aba-4c33-8bed-09b394e935a5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_8931d62f-62c3-44d6-941a-4dd78e73af7e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_8c6900fe-56a6-4ca6-86c7-a58a2e2bec46" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_8931d62f-62c3-44d6-941a-4dd78e73af7e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_f08e55a0-1b24-490d-baa8-3121408e73ad" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_8931d62f-62c3-44d6-941a-4dd78e73af7e" xlink:to="loc_us-gaap_PlanNameAxis_f08e55a0-1b24-490d-baa8-3121408e73ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_f08e55a0-1b24-490d-baa8-3121408e73ad_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_f08e55a0-1b24-490d-baa8-3121408e73ad" xlink:to="loc_us-gaap_PlanNameDomain_f08e55a0-1b24-490d-baa8-3121408e73ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_5290d781-c676-41ab-b6ce-7a153d9f8ec3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_f08e55a0-1b24-490d-baa8-3121408e73ad" xlink:to="loc_us-gaap_PlanNameDomain_5290d781-c676-41ab-b6ce-7a153d9f8ec3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentyIncentiveAwardPlanMember_55fb8f87-b392-4202-bdb9-4c3afebb3cd8" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentyIncentiveAwardPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_5290d781-c676-41ab-b6ce-7a153d9f8ec3" xlink:to="loc_bsy_TwoThousandTwentyIncentiveAwardPlanMember_55fb8f87-b392-4202-bdb9-4c3afebb3cd8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_8bf37779-294d-4177-9dc8-5cadddc16708" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_8931d62f-62c3-44d6-941a-4dd78e73af7e" xlink:to="loc_us-gaap_AwardTypeAxis_8bf37779-294d-4177-9dc8-5cadddc16708" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_8bf37779-294d-4177-9dc8-5cadddc16708_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_8bf37779-294d-4177-9dc8-5cadddc16708" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_8bf37779-294d-4177-9dc8-5cadddc16708_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cdb0bba7-3375-46b7-87f0-002ff0cbb26b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_8bf37779-294d-4177-9dc8-5cadddc16708" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cdb0bba7-3375-46b7-87f0-002ff0cbb26b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_8836ccdc-2d4a-4841-8684-2f15e1e05497" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cdb0bba7-3375-46b7-87f0-002ff0cbb26b" xlink:to="loc_us-gaap_EmployeeStockOptionMember_8836ccdc-2d4a-4841-8684-2f15e1e05497" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/EquityAwardsandInstrumentsStockOptionsNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#EquityAwardsandInstrumentsStockOptionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/EquityAwardsandInstrumentsStockOptionsNarrativeDetails" xlink:type="extended" id="i4e99d58f08d444ecba34a52f649a3f5e_EquityAwardsandInstrumentsStockOptionsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7b85e338-3d58-47db-9610-9c299e18368b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromStockOptionsExercised_cf13adcd-b165-4596-b25b-d47f742110c8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7b85e338-3d58-47db-9610-9c299e18368b" xlink:to="loc_us-gaap_ProceedsFromStockOptionsExercised_cf13adcd-b165-4596-b25b-d47f742110c8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_24127619-abdf-4a21-99f6-279542b9b83f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7b85e338-3d58-47db-9610-9c299e18368b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_24127619-abdf-4a21-99f6-279542b9b83f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_c1f13958-81be-4054-89cc-b9309e1f859b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7b85e338-3d58-47db-9610-9c299e18368b" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_c1f13958-81be-4054-89cc-b9309e1f859b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_a5aca6e5-ac1e-4b76-9305-6bbfc63b0f95" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7b85e338-3d58-47db-9610-9c299e18368b" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_a5aca6e5-ac1e-4b76-9305-6bbfc63b0f95" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_e42f4074-acd4-47a7-abae-6d0ec5d46d70" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_7b85e338-3d58-47db-9610-9c299e18368b" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_e42f4074-acd4-47a7-abae-6d0ec5d46d70" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_0decd9d0-001e-4343-af63-8689d385abca" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_e42f4074-acd4-47a7-abae-6d0ec5d46d70" xlink:to="loc_us-gaap_AwardTypeAxis_0decd9d0-001e-4343-af63-8689d385abca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0decd9d0-001e-4343-af63-8689d385abca_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_0decd9d0-001e-4343-af63-8689d385abca" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0decd9d0-001e-4343-af63-8689d385abca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9570586f-d28b-4cb5-8abb-59d5cef38314" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_0decd9d0-001e-4343-af63-8689d385abca" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9570586f-d28b-4cb5-8abb-59d5cef38314" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_83d5129e-ceba-4ad0-83fe-f14b9566e9c1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9570586f-d28b-4cb5-8abb-59d5cef38314" xlink:to="loc_us-gaap_EmployeeStockOptionMember_83d5129e-ceba-4ad0-83fe-f14b9566e9c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_31422a0f-a597-4b19-bd48-5088449f0d5c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_e42f4074-acd4-47a7-abae-6d0ec5d46d70" xlink:to="loc_us-gaap_PlanNameAxis_31422a0f-a597-4b19-bd48-5088449f0d5c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_31422a0f-a597-4b19-bd48-5088449f0d5c_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_31422a0f-a597-4b19-bd48-5088449f0d5c" xlink:to="loc_us-gaap_PlanNameDomain_31422a0f-a597-4b19-bd48-5088449f0d5c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_667a1cd8-175a-4218-9dcd-950a2b2bb993" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_31422a0f-a597-4b19-bd48-5088449f0d5c" xlink:to="loc_us-gaap_PlanNameDomain_667a1cd8-175a-4218-9dcd-950a2b2bb993" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentyIncentiveAwardPlanMember_7054caa8-2ebb-44a5-8cbc-6304cdf15dc3" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentyIncentiveAwardPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_667a1cd8-175a-4218-9dcd-950a2b2bb993" xlink:to="loc_bsy_TwoThousandTwentyIncentiveAwardPlanMember_7054caa8-2ebb-44a5-8cbc-6304cdf15dc3" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/EquityAwardsandInstrumentsAcquisitionOptionsNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#EquityAwardsandInstrumentsAcquisitionOptionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/EquityAwardsandInstrumentsAcquisitionOptionsNarrativeDetails" xlink:type="extended" id="i7d7fb23d5e56441db62319a694e7fe48_EquityAwardsandInstrumentsAcquisitionOptionsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_344f1adf-a258-4971-979a-dbbb373cdc6b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_d4ed20be-4b86-4907-9903-71dbef2662fc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_344f1adf-a258-4971-979a-dbbb373cdc6b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_d4ed20be-4b86-4907-9903-71dbef2662fc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_84216cdb-c245-4753-b7a0-287849fbd684" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_344f1adf-a258-4971-979a-dbbb373cdc6b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_84216cdb-c245-4753-b7a0-287849fbd684" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_ec0fd6a5-aa50-4215-a6b9-a9eb63713f7e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_344f1adf-a258-4971-979a-dbbb373cdc6b" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_ec0fd6a5-aa50-4215-a6b9-a9eb63713f7e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_fd1b00d3-b7d3-4523-849f-e5193fea9d8d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_344f1adf-a258-4971-979a-dbbb373cdc6b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_fd1b00d3-b7d3-4523-849f-e5193fea9d8d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_341d52fb-3503-4399-8c1a-68a5315ebdb0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_344f1adf-a258-4971-979a-dbbb373cdc6b" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_341d52fb-3503-4399-8c1a-68a5315ebdb0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_9410bee6-c8ff-4294-b021-7985a4eca85f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_344f1adf-a258-4971-979a-dbbb373cdc6b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_9410bee6-c8ff-4294-b021-7985a4eca85f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_3b1f62f6-04bf-4fdb-a6fc-d63ce5a9bb84" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_344f1adf-a258-4971-979a-dbbb373cdc6b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_3b1f62f6-04bf-4fdb-a6fc-d63ce5a9bb84" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b7433f42-b3f3-48a8-b0f1-5648741f874b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_344f1adf-a258-4971-979a-dbbb373cdc6b" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b7433f42-b3f3-48a8-b0f1-5648741f874b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_7cc44b34-efdd-46e9-a3dc-24675ca1aef9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b7433f42-b3f3-48a8-b0f1-5648741f874b" xlink:to="loc_us-gaap_AwardTypeAxis_7cc44b34-efdd-46e9-a3dc-24675ca1aef9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7cc44b34-efdd-46e9-a3dc-24675ca1aef9_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_7cc44b34-efdd-46e9-a3dc-24675ca1aef9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7cc44b34-efdd-46e9-a3dc-24675ca1aef9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5f00093c-fc0c-4a5d-97b4-3d2fb04118df" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_7cc44b34-efdd-46e9-a3dc-24675ca1aef9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5f00093c-fc0c-4a5d-97b4-3d2fb04118df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_c41c2d3a-264c-4cf0-aab5-4e03d730376c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5f00093c-fc0c-4a5d-97b4-3d2fb04118df" xlink:to="loc_us-gaap_EmployeeStockOptionMember_c41c2d3a-264c-4cf0-aab5-4e03d730376c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_38dfd3a1-36a6-4461-b736-8c204b6296b4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b7433f42-b3f3-48a8-b0f1-5648741f874b" xlink:to="loc_us-gaap_PlanNameAxis_38dfd3a1-36a6-4461-b736-8c204b6296b4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_38dfd3a1-36a6-4461-b736-8c204b6296b4_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_38dfd3a1-36a6-4461-b736-8c204b6296b4" xlink:to="loc_us-gaap_PlanNameDomain_38dfd3a1-36a6-4461-b736-8c204b6296b4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_f3ed8f0b-59d1-436f-83dd-559e52632745" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_38dfd3a1-36a6-4461-b736-8c204b6296b4" xlink:to="loc_us-gaap_PlanNameDomain_f3ed8f0b-59d1-436f-83dd-559e52632745" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_EquityIncentivePlanMember_57765ddf-3fe7-4ca1-93f8-4b5cba922316" xlink:href="bsy-20210630.xsd#bsy_EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_f3ed8f0b-59d1-436f-83dd-559e52632745" xlink:to="loc_bsy_EquityIncentivePlanMember_57765ddf-3fe7-4ca1-93f8-4b5cba922316" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_ce6cba15-f131-4dce-a9fe-f1833b76c119" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b7433f42-b3f3-48a8-b0f1-5648741f874b" xlink:to="loc_us-gaap_StatementClassOfStockAxis_ce6cba15-f131-4dce-a9fe-f1833b76c119" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_ce6cba15-f131-4dce-a9fe-f1833b76c119_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_ce6cba15-f131-4dce-a9fe-f1833b76c119" xlink:to="loc_us-gaap_ClassOfStockDomain_ce6cba15-f131-4dce-a9fe-f1833b76c119_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_9bf01640-b43b-4576-b621-54873b257726" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_ce6cba15-f131-4dce-a9fe-f1833b76c119" xlink:to="loc_us-gaap_ClassOfStockDomain_9bf01640-b43b-4576-b621-54873b257726" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_30a3bbe6-a50f-42ac-a9ec-cda43c0a8f2a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_9bf01640-b43b-4576-b621-54873b257726" xlink:to="loc_us-gaap_CommonClassBMember_30a3bbe6-a50f-42ac-a9ec-cda43c0a8f2a" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/EquityAwardsandInstrumentsRestrictedStockandRSUsActivityDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#EquityAwardsandInstrumentsRestrictedStockandRSUsActivityDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/EquityAwardsandInstrumentsRestrictedStockandRSUsActivityDetails" xlink:type="extended" id="ib9a8ad8ebe6a463a9e3ba5fa242bd4e5_EquityAwardsandInstrumentsRestrictedStockandRSUsActivityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_11d67267-6c92-4d5b-b870-110052737e90" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_e3b2affa-63f0-42f5-8fa4-d37f0a9cbfc6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_11d67267-6c92-4d5b-b870-110052737e90" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_e3b2affa-63f0-42f5-8fa4-d37f0a9cbfc6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_43132e42-d647-4776-99ab-5c2ec54deb3a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_e3b2affa-63f0-42f5-8fa4-d37f0a9cbfc6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_43132e42-d647-4776-99ab-5c2ec54deb3a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_b81fc620-0e1e-48ff-a0cd-12ecd3c66026" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_e3b2affa-63f0-42f5-8fa4-d37f0a9cbfc6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_b81fc620-0e1e-48ff-a0cd-12ecd3c66026" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_e06f611d-73dc-4251-a0d2-5750a1b431fe" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_e3b2affa-63f0-42f5-8fa4-d37f0a9cbfc6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_e06f611d-73dc-4251-a0d2-5750a1b431fe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_69083cad-db8d-4321-b881-b7c850dc2d1b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_e3b2affa-63f0-42f5-8fa4-d37f0a9cbfc6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_69083cad-db8d-4321-b881-b7c850dc2d1b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_276fbb6a-7d23-4ad7-b8dc-be34f32240c7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cd5ead1c-4191-4d7e-8a02-b8ee06132b7f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_11d67267-6c92-4d5b-b870-110052737e90" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cd5ead1c-4191-4d7e-8a02-b8ee06132b7f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_b3faea5d-d7ac-4650-ac20-8cd9d592e19d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cd5ead1c-4191-4d7e-8a02-b8ee06132b7f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_b3faea5d-d7ac-4650-ac20-8cd9d592e19d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_c498fa39-4874-4124-b6ce-da03be63a4aa" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cd5ead1c-4191-4d7e-8a02-b8ee06132b7f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_c498fa39-4874-4124-b6ce-da03be63a4aa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_bd9aca00-6b0f-48cf-b3cc-bab06b1fdf19" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cd5ead1c-4191-4d7e-8a02-b8ee06132b7f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_bd9aca00-6b0f-48cf-b3cc-bab06b1fdf19" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_631116c4-f0c6-465b-b0d7-120b23cbda35" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_cd5ead1c-4191-4d7e-8a02-b8ee06132b7f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_631116c4-f0c6-465b-b0d7-120b23cbda35" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_fce075fa-ca68-4bc9-9c72-0417e873d94f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d39aeea6-6cf4-4a2c-8fda-9b3bcca3e174" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_11d67267-6c92-4d5b-b870-110052737e90" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d39aeea6-6cf4-4a2c-8fda-9b3bcca3e174" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_58fffd9e-fa27-4410-901a-14453fd9afdb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d39aeea6-6cf4-4a2c-8fda-9b3bcca3e174" xlink:to="loc_us-gaap_AwardTypeAxis_58fffd9e-fa27-4410-901a-14453fd9afdb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_58fffd9e-fa27-4410-901a-14453fd9afdb_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_58fffd9e-fa27-4410-901a-14453fd9afdb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_58fffd9e-fa27-4410-901a-14453fd9afdb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3ff4813e-ff4b-4b46-b16c-6700a85fe234" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_58fffd9e-fa27-4410-901a-14453fd9afdb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3ff4813e-ff4b-4b46-b16c-6700a85fe234" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_RestrictedStockAndRestrictedStockUnitsRSUsMember_91de9e5c-e1cc-4699-a3ec-6de5997f8bc3" xlink:href="bsy-20210630.xsd#bsy_RestrictedStockAndRestrictedStockUnitsRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3ff4813e-ff4b-4b46-b16c-6700a85fe234" xlink:to="loc_bsy_RestrictedStockAndRestrictedStockUnitsRSUsMember_91de9e5c-e1cc-4699-a3ec-6de5997f8bc3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TimeBasedRestrictedStockAndRestrictedStockUnitsRSUsMember_3927884b-c800-4b5d-a941-45e475c16eef" xlink:href="bsy-20210630.xsd#bsy_TimeBasedRestrictedStockAndRestrictedStockUnitsRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3ff4813e-ff4b-4b46-b16c-6700a85fe234" xlink:to="loc_bsy_TimeBasedRestrictedStockAndRestrictedStockUnitsRSUsMember_3927884b-c800-4b5d-a941-45e475c16eef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_PerformanceBasedRestrictedStockAndRestrictedStockUnitsRSUsMember_9ab1c0ed-c411-4266-88f7-18f8053b1393" xlink:href="bsy-20210630.xsd#bsy_PerformanceBasedRestrictedStockAndRestrictedStockUnitsRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3ff4813e-ff4b-4b46-b16c-6700a85fe234" xlink:to="loc_bsy_PerformanceBasedRestrictedStockAndRestrictedStockUnitsRSUsMember_9ab1c0ed-c411-4266-88f7-18f8053b1393" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_CashSettledRestrictedStockUnitsRSUsMember_e4ceb15f-1aa8-49e2-81c6-fd469ca58e57" xlink:href="bsy-20210630.xsd#bsy_CashSettledRestrictedStockUnitsRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3ff4813e-ff4b-4b46-b16c-6700a85fe234" xlink:to="loc_bsy_CashSettledRestrictedStockUnitsRSUsMember_e4ceb15f-1aa8-49e2-81c6-fd469ca58e57" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_5945388a-7806-44c4-a2f7-ee6913693313" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3ff4813e-ff4b-4b46-b16c-6700a85fe234" xlink:to="loc_us-gaap_RestrictedStockMember_5945388a-7806-44c4-a2f7-ee6913693313" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_6c7c394a-9cf7-43ac-b556-88c6bc54dd43" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d39aeea6-6cf4-4a2c-8fda-9b3bcca3e174" xlink:to="loc_us-gaap_PlanNameAxis_6c7c394a-9cf7-43ac-b556-88c6bc54dd43" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_6c7c394a-9cf7-43ac-b556-88c6bc54dd43_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_6c7c394a-9cf7-43ac-b556-88c6bc54dd43" xlink:to="loc_us-gaap_PlanNameDomain_6c7c394a-9cf7-43ac-b556-88c6bc54dd43_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_9f4ab051-e5aa-4b9e-bf47-8b6f3b4177f3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_6c7c394a-9cf7-43ac-b556-88c6bc54dd43" xlink:to="loc_us-gaap_PlanNameDomain_9f4ab051-e5aa-4b9e-bf47-8b6f3b4177f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentyIncentiveAwardPlanMember_07956f99-c8c3-4664-aa26-d2d1f9550559" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentyIncentiveAwardPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_9f4ab051-e5aa-4b9e-bf47-8b6f3b4177f3" xlink:to="loc_bsy_TwoThousandTwentyIncentiveAwardPlanMember_07956f99-c8c3-4664-aa26-d2d1f9550559" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/EquityAwardsandInstrumentsRestrictedStockandRestrictedStockUnitsNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#EquityAwardsandInstrumentsRestrictedStockandRestrictedStockUnitsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/EquityAwardsandInstrumentsRestrictedStockandRestrictedStockUnitsNarrativeDetails" xlink:type="extended" id="ic3056bec6a8a44feabb71fdf86f6edfd_EquityAwardsandInstrumentsRestrictedStockandRestrictedStockUnitsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2288462f-e5d3-4c9a-94b2-95139975bbfc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_1ec4c69e-d42b-486a-8828-7bc3a7b67b15" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2288462f-e5d3-4c9a-94b2-95139975bbfc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_1ec4c69e-d42b-486a-8828-7bc3a7b67b15" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_8464fa26-74ab-4d1d-bd29-3f14949e254f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2288462f-e5d3-4c9a-94b2-95139975bbfc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_8464fa26-74ab-4d1d-bd29-3f14949e254f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsDeliveredInPeriod_e7916d90-c94e-4c4d-b6d0-95c5bf2bd670" xlink:href="bsy-20210630.xsd#bsy_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsDeliveredInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2288462f-e5d3-4c9a-94b2-95139975bbfc" xlink:to="loc_bsy_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsDeliveredInPeriod_e7916d90-c94e-4c4d-b6d0-95c5bf2bd670" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsEarnedThroughDividendsInPeriod_e7cf82ef-ec0a-4a0b-a478-680222ba1567" xlink:href="bsy-20210630.xsd#bsy_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsEarnedThroughDividendsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2288462f-e5d3-4c9a-94b2-95139975bbfc" xlink:to="loc_bsy_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsEarnedThroughDividendsInPeriod_e7cf82ef-ec0a-4a0b-a478-680222ba1567" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_e7a543a1-ba23-404a-b82a-2575cabc7095" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2288462f-e5d3-4c9a-94b2-95139975bbfc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_e7a543a1-ba23-404a-b82a-2575cabc7095" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_1818033f-8aaa-4f36-aba6-04a809f98cfc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2288462f-e5d3-4c9a-94b2-95139975bbfc" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_1818033f-8aaa-4f36-aba6-04a809f98cfc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareBasedLiabilitiesPaid_042d535c-3180-4374-85c8-cfbcce747cad" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareBasedLiabilitiesPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2288462f-e5d3-4c9a-94b2-95139975bbfc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsShareBasedLiabilitiesPaid_042d535c-3180-4374-85c8-cfbcce747cad" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_067459c3-e0ad-4eb6-855b-4bbbaf4e9e80" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2288462f-e5d3-4c9a-94b2-95139975bbfc" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_067459c3-e0ad-4eb6-855b-4bbbaf4e9e80" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_22e0b274-2225-41ea-a6fe-93d4155cca53" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2288462f-e5d3-4c9a-94b2-95139975bbfc" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_22e0b274-2225-41ea-a6fe-93d4155cca53" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_80c583a6-b7c2-456f-99af-07d5c5bb0e1c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2288462f-e5d3-4c9a-94b2-95139975bbfc" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_80c583a6-b7c2-456f-99af-07d5c5bb0e1c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_3ce28561-3c50-4f8b-a31c-ade0aa7e14b1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_80c583a6-b7c2-456f-99af-07d5c5bb0e1c" xlink:to="loc_us-gaap_AwardTypeAxis_3ce28561-3c50-4f8b-a31c-ade0aa7e14b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3ce28561-3c50-4f8b-a31c-ade0aa7e14b1_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_3ce28561-3c50-4f8b-a31c-ade0aa7e14b1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3ce28561-3c50-4f8b-a31c-ade0aa7e14b1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_96eb375c-7804-4171-bff6-4d880937c89e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_3ce28561-3c50-4f8b-a31c-ade0aa7e14b1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_96eb375c-7804-4171-bff6-4d880937c89e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_9045e280-c3cd-4871-98f6-0a0b001a5541" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_96eb375c-7804-4171-bff6-4d880937c89e" xlink:to="loc_us-gaap_RestrictedStockMember_9045e280-c3cd-4871-98f6-0a0b001a5541" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_PerformanceBasedRestrictedStockUnitsRSUsTwoThousandSixteenMember_74243e7e-0adb-498b-9da3-2a6853244b8e" xlink:href="bsy-20210630.xsd#bsy_PerformanceBasedRestrictedStockUnitsRSUsTwoThousandSixteenMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_96eb375c-7804-4171-bff6-4d880937c89e" xlink:to="loc_bsy_PerformanceBasedRestrictedStockUnitsRSUsTwoThousandSixteenMember_74243e7e-0adb-498b-9da3-2a6853244b8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_7c6c2735-672d-4291-a411-e35d94340be9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_96eb375c-7804-4171-bff6-4d880937c89e" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_7c6c2735-672d-4291-a411-e35d94340be9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_RestrictedStockAndRestrictedStockUnitsRSUsMember_ad9bbf41-15e5-48b5-b1c3-11b80dfe4b5c" xlink:href="bsy-20210630.xsd#bsy_RestrictedStockAndRestrictedStockUnitsRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_96eb375c-7804-4171-bff6-4d880937c89e" xlink:to="loc_bsy_RestrictedStockAndRestrictedStockUnitsRSUsMember_ad9bbf41-15e5-48b5-b1c3-11b80dfe4b5c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TimeBasedRestrictedStockAndRestrictedStockUnitsRSUsMember_c5eda3f0-3163-48c0-b36a-96f1a43db162" xlink:href="bsy-20210630.xsd#bsy_TimeBasedRestrictedStockAndRestrictedStockUnitsRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_96eb375c-7804-4171-bff6-4d880937c89e" xlink:to="loc_bsy_TimeBasedRestrictedStockAndRestrictedStockUnitsRSUsMember_c5eda3f0-3163-48c0-b36a-96f1a43db162" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_PerformanceBasedRestrictedStockAndRestrictedStockUnitsRSUsMember_26572d8d-428d-48a8-9178-2a4f17e46e0a" xlink:href="bsy-20210630.xsd#bsy_PerformanceBasedRestrictedStockAndRestrictedStockUnitsRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_96eb375c-7804-4171-bff6-4d880937c89e" xlink:to="loc_bsy_PerformanceBasedRestrictedStockAndRestrictedStockUnitsRSUsMember_26572d8d-428d-48a8-9178-2a4f17e46e0a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_ef61253d-1be0-4bd7-9938-702b2d89a04f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_80c583a6-b7c2-456f-99af-07d5c5bb0e1c" xlink:to="loc_us-gaap_PlanNameAxis_ef61253d-1be0-4bd7-9938-702b2d89a04f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_ef61253d-1be0-4bd7-9938-702b2d89a04f_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_ef61253d-1be0-4bd7-9938-702b2d89a04f" xlink:to="loc_us-gaap_PlanNameDomain_ef61253d-1be0-4bd7-9938-702b2d89a04f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_3293d7af-c1dd-4a77-a85e-b44913479c08" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_ef61253d-1be0-4bd7-9938-702b2d89a04f" xlink:to="loc_us-gaap_PlanNameDomain_3293d7af-c1dd-4a77-a85e-b44913479c08" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentyIncentiveAwardPlanMember_c52b80a9-a9bd-45fc-8162-bf6697fb80e5" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentyIncentiveAwardPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_3293d7af-c1dd-4a77-a85e-b44913479c08" xlink:to="loc_bsy_TwoThousandTwentyIncentiveAwardPlanMember_c52b80a9-a9bd-45fc-8162-bf6697fb80e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_ec10e6da-e72a-4deb-b3f5-d18c2d42dbe1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_80c583a6-b7c2-456f-99af-07d5c5bb0e1c" xlink:to="loc_us-gaap_VestingAxis_ec10e6da-e72a-4deb-b3f5-d18c2d42dbe1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_ec10e6da-e72a-4deb-b3f5-d18c2d42dbe1_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_ec10e6da-e72a-4deb-b3f5-d18c2d42dbe1" xlink:to="loc_us-gaap_VestingDomain_ec10e6da-e72a-4deb-b3f5-d18c2d42dbe1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_4a4e831b-4912-4c09-af68-94fcdc60a570" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_ec10e6da-e72a-4deb-b3f5-d18c2d42dbe1" xlink:to="loc_us-gaap_VestingDomain_4a4e831b-4912-4c09-af68-94fcdc60a570" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_PerformanceBasedVestingMember_37bbc0cf-2a0b-48c1-be9f-b2e356f64862" xlink:href="bsy-20210630.xsd#bsy_PerformanceBasedVestingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_4a4e831b-4912-4c09-af68-94fcdc60a570" xlink:to="loc_bsy_PerformanceBasedVestingMember_37bbc0cf-2a0b-48c1-be9f-b2e356f64862" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/EquityAwardsandInstrumentsStockGrantsNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#EquityAwardsandInstrumentsStockGrantsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/EquityAwardsandInstrumentsStockGrantsNarrativeDetails" xlink:type="extended" id="ie35c72d699484468bf11a1f09bbb4298_EquityAwardsandInstrumentsStockGrantsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_89427a1b-e0f3-416b-b6d2-e26ef358700e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_105b1e90-9f27-4b4d-aa74-17f5ca1c681e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_89427a1b-e0f3-416b-b6d2-e26ef358700e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_105b1e90-9f27-4b4d-aa74-17f5ca1c681e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_905ff564-8589-4353-8252-375a5058a73b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_89427a1b-e0f3-416b-b6d2-e26ef358700e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_905ff564-8589-4353-8252-375a5058a73b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_328b38ef-1a93-4505-9fbc-29a2de04113a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_89427a1b-e0f3-416b-b6d2-e26ef358700e" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_328b38ef-1a93-4505-9fbc-29a2de04113a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_0e96497e-2fd2-4bfd-93e7-8e7ad7801f2e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_328b38ef-1a93-4505-9fbc-29a2de04113a" xlink:to="loc_us-gaap_AwardTypeAxis_0e96497e-2fd2-4bfd-93e7-8e7ad7801f2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0e96497e-2fd2-4bfd-93e7-8e7ad7801f2e_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_0e96497e-2fd2-4bfd-93e7-8e7ad7801f2e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0e96497e-2fd2-4bfd-93e7-8e7ad7801f2e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5d9de3a0-becb-4639-8eab-926766d018ce" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_0e96497e-2fd2-4bfd-93e7-8e7ad7801f2e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5d9de3a0-becb-4639-8eab-926766d018ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_d346a097-fe75-4007-9b41-18c52fdee720" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5d9de3a0-becb-4639-8eab-926766d018ce" xlink:to="loc_us-gaap_CommonClassBMember_d346a097-fe75-4007-9b41-18c52fdee720" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_53d903c8-278b-4c02-9989-19eabf149af4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_328b38ef-1a93-4505-9fbc-29a2de04113a" xlink:to="loc_us-gaap_PlanNameAxis_53d903c8-278b-4c02-9989-19eabf149af4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_53d903c8-278b-4c02-9989-19eabf149af4_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_53d903c8-278b-4c02-9989-19eabf149af4" xlink:to="loc_us-gaap_PlanNameDomain_53d903c8-278b-4c02-9989-19eabf149af4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_a38358e9-ed4a-4fbd-ad74-9041ad9c0728" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_53d903c8-278b-4c02-9989-19eabf149af4" xlink:to="loc_us-gaap_PlanNameDomain_a38358e9-ed4a-4fbd-ad74-9041ad9c0728" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentyIncentiveAwardPlanMember_c76a106e-dd2b-4815-9046-9d17db46bfab" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentyIncentiveAwardPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_a38358e9-ed4a-4fbd-ad74-9041ad9c0728" xlink:to="loc_bsy_TwoThousandTwentyIncentiveAwardPlanMember_c76a106e-dd2b-4815-9046-9d17db46bfab" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/EquityAwardsandInstrumentsEquityAwardsSubsequentToJune302021NarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#EquityAwardsandInstrumentsEquityAwardsSubsequentToJune302021NarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/EquityAwardsandInstrumentsEquityAwardsSubsequentToJune302021NarrativeDetails" xlink:type="extended" id="id653a7b2cc03460b92f166ff110d3c9d_EquityAwardsandInstrumentsEquityAwardsSubsequentToJune302021NarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_da1b2e8f-474d-4510-81f7-bb6e51905572" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_184b3f6e-f1d1-4f97-ac7f-8fb3321b1490" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_da1b2e8f-474d-4510-81f7-bb6e51905572" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_184b3f6e-f1d1-4f97-ac7f-8fb3321b1490" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_7695af3e-54f3-499c-9cc1-04a5a4e31fc8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_da1b2e8f-474d-4510-81f7-bb6e51905572" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_7695af3e-54f3-499c-9cc1-04a5a4e31fc8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_9e53ffab-42eb-4b61-8acd-3f1a6f8d74bb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_da1b2e8f-474d-4510-81f7-bb6e51905572" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_9e53ffab-42eb-4b61-8acd-3f1a6f8d74bb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c0cb8243-7248-4387-aeb7-ce5d1f89e6e6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_da1b2e8f-474d-4510-81f7-bb6e51905572" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c0cb8243-7248-4387-aeb7-ce5d1f89e6e6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_cca2db14-0156-4ec8-b9c4-5a9494ecbdd0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c0cb8243-7248-4387-aeb7-ce5d1f89e6e6" xlink:to="loc_us-gaap_AwardTypeAxis_cca2db14-0156-4ec8-b9c4-5a9494ecbdd0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cca2db14-0156-4ec8-b9c4-5a9494ecbdd0_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_cca2db14-0156-4ec8-b9c4-5a9494ecbdd0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_cca2db14-0156-4ec8-b9c4-5a9494ecbdd0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_af0a85e1-197f-4545-b6a1-99af39632ee0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_cca2db14-0156-4ec8-b9c4-5a9494ecbdd0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_af0a85e1-197f-4545-b6a1-99af39632ee0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TimeBasedRestrictedStockUnitsRSUsMember_74e4faca-7eb4-473d-b208-00d7883a5655" xlink:href="bsy-20210630.xsd#bsy_TimeBasedRestrictedStockUnitsRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_af0a85e1-197f-4545-b6a1-99af39632ee0" xlink:to="loc_bsy_TimeBasedRestrictedStockUnitsRSUsMember_74e4faca-7eb4-473d-b208-00d7883a5655" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_aa8ea1e4-dd6a-4b8f-b098-5d40f022e9bf" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c0cb8243-7248-4387-aeb7-ce5d1f89e6e6" xlink:to="loc_us-gaap_PlanNameAxis_aa8ea1e4-dd6a-4b8f-b098-5d40f022e9bf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_aa8ea1e4-dd6a-4b8f-b098-5d40f022e9bf_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_aa8ea1e4-dd6a-4b8f-b098-5d40f022e9bf" xlink:to="loc_us-gaap_PlanNameDomain_aa8ea1e4-dd6a-4b8f-b098-5d40f022e9bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_6a6d66e9-0513-4411-af5a-1a383f143a40" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_aa8ea1e4-dd6a-4b8f-b098-5d40f022e9bf" xlink:to="loc_us-gaap_PlanNameDomain_6a6d66e9-0513-4411-af5a-1a383f143a40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentyIncentiveAwardPlanMember_6916ce64-0bfe-4a66-a881-07cee870f995" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentyIncentiveAwardPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_6a6d66e9-0513-4411-af5a-1a383f143a40" xlink:to="loc_bsy_TwoThousandTwentyIncentiveAwardPlanMember_6916ce64-0bfe-4a66-a881-07cee870f995" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_4c3420d4-9b06-4385-bfbe-571ffe4a4bf5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c0cb8243-7248-4387-aeb7-ce5d1f89e6e6" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_4c3420d4-9b06-4385-bfbe-571ffe4a4bf5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_4c3420d4-9b06-4385-bfbe-571ffe4a4bf5_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_4c3420d4-9b06-4385-bfbe-571ffe4a4bf5" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_4c3420d4-9b06-4385-bfbe-571ffe4a4bf5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_81a508f3-b105-4bbd-a921-1f44499288a9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_4c3420d4-9b06-4385-bfbe-571ffe4a4bf5" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_81a508f3-b105-4bbd-a921-1f44499288a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_68edff06-ec0a-44d2-874b-46743b89e003" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_81a508f3-b105-4bbd-a921-1f44499288a9" xlink:to="loc_us-gaap_SubsequentEventMember_68edff06-ec0a-44d2-874b-46743b89e003" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/FairValueofFinancialInstrumentsNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#FairValueofFinancialInstrumentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/FairValueofFinancialInstrumentsNarrativeDetails" xlink:type="extended" id="iba0e409a00da40159fcb559e8968c797_FairValueofFinancialInstrumentsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_86990871-0413-472c-8fe8-51eee4db894d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityNotionalAmount_fd37208c-f228-4ab7-9245-24344dce3358" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeLiabilityNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_86990871-0413-472c-8fe8-51eee4db894d" xlink:to="loc_us-gaap_DerivativeLiabilityNotionalAmount_fd37208c-f228-4ab7-9245-24344dce3358" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTermOfContract_9bdb7954-e56b-4472-9ed0-c8aabad257a8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_86990871-0413-472c-8fe8-51eee4db894d" xlink:to="loc_us-gaap_DerivativeTermOfContract_9bdb7954-e56b-4472-9ed0-c8aabad257a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_298cc994-d96d-4846-8447-15d101803a0f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_86990871-0413-472c-8fe8-51eee4db894d" xlink:to="loc_us-gaap_LongTermDebtFairValue_298cc994-d96d-4846-8447-15d101803a0f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_33206580-587b-49d2-a3de-a0c3fae30c73" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_86990871-0413-472c-8fe8-51eee4db894d" xlink:to="loc_us-gaap_DerivativeTable_33206580-587b-49d2-a3de-a0c3fae30c73" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_bb5470fa-358b-4860-a106-6aeabffd97a2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_33206580-587b-49d2-a3de-a0c3fae30c73" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_bb5470fa-358b-4860-a106-6aeabffd97a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_bb5470fa-358b-4860-a106-6aeabffd97a2_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_bb5470fa-358b-4860-a106-6aeabffd97a2" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_bb5470fa-358b-4860-a106-6aeabffd97a2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_978d50c2-f7f0-4403-b999-e907986e8c3c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_bb5470fa-358b-4860-a106-6aeabffd97a2" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_978d50c2-f7f0-4403-b999-e907986e8c3c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_0612f67d-f5af-46e9-8dbf-b8a1c5e74b9e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_978d50c2-f7f0-4403-b999-e907986e8c3c" xlink:to="loc_us-gaap_InterestRateSwapMember_0612f67d-f5af-46e9-8dbf-b8a1c5e74b9e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_1a18f076-41fe-42d4-8437-f07920813c12" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_33206580-587b-49d2-a3de-a0c3fae30c73" xlink:to="loc_us-gaap_HedgingDesignationAxis_1a18f076-41fe-42d4-8437-f07920813c12" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_1a18f076-41fe-42d4-8437-f07920813c12_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_1a18f076-41fe-42d4-8437-f07920813c12" xlink:to="loc_us-gaap_HedgingDesignationDomain_1a18f076-41fe-42d4-8437-f07920813c12_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_8c1c2868-3dd5-46d3-8bb0-6406e3e8117c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_1a18f076-41fe-42d4-8437-f07920813c12" xlink:to="loc_us-gaap_HedgingDesignationDomain_8c1c2868-3dd5-46d3-8bb0-6406e3e8117c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_41ab3404-7b3e-43fa-97cf-62d4f72e758d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_8c1c2868-3dd5-46d3-8bb0-6406e3e8117c" xlink:to="loc_us-gaap_NondesignatedMember_41ab3404-7b3e-43fa-97cf-62d4f72e758d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_a913be79-7160-4692-a7c2-67447e724895" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_33206580-587b-49d2-a3de-a0c3fae30c73" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_a913be79-7160-4692-a7c2-67447e724895" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_a913be79-7160-4692-a7c2-67447e724895_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_a913be79-7160-4692-a7c2-67447e724895" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_a913be79-7160-4692-a7c2-67447e724895_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_22fc0a07-7530-4305-9fd4-65dc197734b8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_a913be79-7160-4692-a7c2-67447e724895" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_22fc0a07-7530-4305-9fd4-65dc197734b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_419b4886-1d30-4e96-a89d-9d5b60a0e11a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_22fc0a07-7530-4305-9fd4-65dc197734b8" xlink:to="loc_us-gaap_ConvertibleDebtMember_419b4886-1d30-4e96-a89d-9d5b60a0e11a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_23392d2e-7357-40af-961d-3dd923467f8b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_33206580-587b-49d2-a3de-a0c3fae30c73" xlink:to="loc_us-gaap_DebtInstrumentAxis_23392d2e-7357-40af-961d-3dd923467f8b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_23392d2e-7357-40af-961d-3dd923467f8b_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_23392d2e-7357-40af-961d-3dd923467f8b" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_23392d2e-7357-40af-961d-3dd923467f8b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_6fc9e405-62e2-4c8e-82ca-aafaae843bfc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_23392d2e-7357-40af-961d-3dd923467f8b" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_6fc9e405-62e2-4c8e-82ca-aafaae843bfc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentySixNotesMember_b0a8d5d7-97b3-4980-91c6-c6e8dcf0fddb" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentySixNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_6fc9e405-62e2-4c8e-82ca-aafaae843bfc" xlink:to="loc_bsy_TwoThousandTwentySixNotesMember_b0a8d5d7-97b3-4980-91c6-c6e8dcf0fddb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentySevenNotesMember_8eb05be5-a29f-4673-850a-da30181284d3" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentySevenNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_6fc9e405-62e2-4c8e-82ca-aafaae843bfc" xlink:to="loc_bsy_TwoThousandTwentySevenNotesMember_8eb05be5-a29f-4673-850a-da30181284d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_46c36da4-c4e3-48bf-93d9-4a161bd96060" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_33206580-587b-49d2-a3de-a0c3fae30c73" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_46c36da4-c4e3-48bf-93d9-4a161bd96060" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_46c36da4-c4e3-48bf-93d9-4a161bd96060_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_46c36da4-c4e3-48bf-93d9-4a161bd96060" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_46c36da4-c4e3-48bf-93d9-4a161bd96060_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f672d580-9b0e-4776-a924-35c6c68d1ac4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_46c36da4-c4e3-48bf-93d9-4a161bd96060" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f672d580-9b0e-4776-a924-35c6c68d1ac4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_8c1eec92-f94d-4eed-8b0b-af4213dfcd94" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f672d580-9b0e-4776-a924-35c6c68d1ac4" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_8c1eec92-f94d-4eed-8b0b-af4213dfcd94" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/FairValueofFinancialInstrumentsInterestRateSwapActivityDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#FairValueofFinancialInstrumentsInterestRateSwapActivityDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/FairValueofFinancialInstrumentsInterestRateSwapActivityDetails" xlink:type="extended" id="i9297c4f993eb45b1afcb2abe0d85b9a5_FairValueofFinancialInstrumentsInterestRateSwapActivityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_6b72a213-25a1-4847-8372-006d9bf9800f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_3d0a2dfa-3ed9-414a-a2ff-cfb0b0a1cfca" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_6b72a213-25a1-4847-8372-006d9bf9800f" xlink:to="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_3d0a2dfa-3ed9-414a-a2ff-cfb0b0a1cfca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsPayments_f907f593-d2d9-4fa6-bdeb-d91c37e981bc" xlink:href="bsy-20210630.xsd#bsy_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_6b72a213-25a1-4847-8372-006d9bf9800f" xlink:to="loc_bsy_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsPayments_f907f593-d2d9-4fa6-bdeb-d91c37e981bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_1f6218eb-c31c-465f-894e-56d5d372a329" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_6b72a213-25a1-4847-8372-006d9bf9800f" xlink:to="loc_us-gaap_DerivativeTable_1f6218eb-c31c-465f-894e-56d5d372a329" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_aeef72c6-b4e6-4bb6-a1f8-c4c6ed7d26cd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_1f6218eb-c31c-465f-894e-56d5d372a329" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_aeef72c6-b4e6-4bb6-a1f8-c4c6ed7d26cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_aeef72c6-b4e6-4bb6-a1f8-c4c6ed7d26cd_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_aeef72c6-b4e6-4bb6-a1f8-c4c6ed7d26cd" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_aeef72c6-b4e6-4bb6-a1f8-c4c6ed7d26cd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_325f8679-543f-4de5-897c-62a97854c785" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_aeef72c6-b4e6-4bb6-a1f8-c4c6ed7d26cd" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_325f8679-543f-4de5-897c-62a97854c785" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_76f30666-8d22-48b9-a882-b6b638b1df82" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_325f8679-543f-4de5-897c-62a97854c785" xlink:to="loc_us-gaap_InterestRateSwapMember_76f30666-8d22-48b9-a882-b6b638b1df82" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_239fde23-c72f-41df-aeb7-ed7b99cacdb4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_1f6218eb-c31c-465f-894e-56d5d372a329" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_239fde23-c72f-41df-aeb7-ed7b99cacdb4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_239fde23-c72f-41df-aeb7-ed7b99cacdb4_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_239fde23-c72f-41df-aeb7-ed7b99cacdb4" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_239fde23-c72f-41df-aeb7-ed7b99cacdb4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_72fab416-c3d2-4180-9ccd-1c0378c4cb16" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_239fde23-c72f-41df-aeb7-ed7b99cacdb4" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_72fab416-c3d2-4180-9ccd-1c0378c4cb16" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpenseMember_7f9c0ae9-2dbf-4f5a-90c4-070385c776c1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_72fab416-c3d2-4180-9ccd-1c0378c4cb16" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpenseMember_7f9c0ae9-2dbf-4f5a-90c4-070385c776c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseMember_cd07b455-a250-4ead-b133-1bbee064949f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_72fab416-c3d2-4180-9ccd-1c0378c4cb16" xlink:to="loc_us-gaap_InterestExpenseMember_cd07b455-a250-4ead-b133-1bbee064949f" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/FairValueofFinancialInstrumentsFairValueofFinancialAssetsandLiabilitiesDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#FairValueofFinancialInstrumentsFairValueofFinancialAssetsandLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/FairValueofFinancialInstrumentsFairValueofFinancialAssetsandLiabilitiesDetails" xlink:type="extended" id="ie66f0e1b05f04ba8b15330e004d7f7e8_FairValueofFinancialInstrumentsFairValueofFinancialAssetsandLiabilitiesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f8df9848-528c-4eae-b1b0-964117e8f372" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_bb3b2d30-a59c-44fe-b3ad-b971f067a012" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f8df9848-528c-4eae-b1b0-964117e8f372" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_bb3b2d30-a59c-44fe-b3ad-b971f067a012" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_4a13b7b1-5280-447f-b0a9-837bcddb6da0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_bb3b2d30-a59c-44fe-b3ad-b971f067a012" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_4a13b7b1-5280-447f-b0a9-837bcddb6da0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_d845b8f3-aef7-4c96-b676-e933248abd46" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_bb3b2d30-a59c-44fe-b3ad-b971f067a012" xlink:to="loc_us-gaap_DerivativeAssets_d845b8f3-aef7-4c96-b676-e933248abd46" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_6797a006-53f9-4569-9f60-16b2c07c2a3e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_bb3b2d30-a59c-44fe-b3ad-b971f067a012" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_6797a006-53f9-4569-9f60-16b2c07c2a3e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_bbe90558-66f5-480d-8813-4feb7a0d9e17" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f8df9848-528c-4eae-b1b0-964117e8f372" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_bbe90558-66f5-480d-8813-4feb7a0d9e17" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_58b60bbe-e03e-4ed5-aad3-93377acc00e3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_bbe90558-66f5-480d-8813-4feb7a0d9e17" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_58b60bbe-e03e-4ed5-aad3-93377acc00e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DeferredCompensationLiabilityFairValueDisclosure_db465ede-738a-45c1-85b8-920105e2df12" xlink:href="bsy-20210630.xsd#bsy_DeferredCompensationLiabilityFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_bbe90558-66f5-480d-8813-4feb7a0d9e17" xlink:to="loc_bsy_DeferredCompensationLiabilityFairValueDisclosure_db465ede-738a-45c1-85b8-920105e2df12" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_AccruedEquityBasedCompensationFairValueDisclosure_5f4717f4-e727-4550-a861-b3c8600f546f" xlink:href="bsy-20210630.xsd#bsy_AccruedEquityBasedCompensationFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_bbe90558-66f5-480d-8813-4feb7a0d9e17" xlink:to="loc_bsy_AccruedEquityBasedCompensationFairValueDisclosure_5f4717f4-e727-4550-a861-b3c8600f546f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_22a1af13-864a-480d-a6f4-47de77cbf6a9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_bbe90558-66f5-480d-8813-4feb7a0d9e17" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_22a1af13-864a-480d-a6f4-47de77cbf6a9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent_228c7a8d-3aab-46d9-9dc4-101ba54c4e18" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f8df9848-528c-4eae-b1b0-964117e8f372" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent_228c7a8d-3aab-46d9-9dc4-101ba54c4e18" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DeferredCompensationLiabilityFairValueDisclosureCurrent_1c8b83cb-c110-4865-8e28-6ddc8e8b0822" xlink:href="bsy-20210630.xsd#bsy_DeferredCompensationLiabilityFairValueDisclosureCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f8df9848-528c-4eae-b1b0-964117e8f372" xlink:to="loc_bsy_DeferredCompensationLiabilityFairValueDisclosureCurrent_1c8b83cb-c110-4865-8e28-6ddc8e8b0822" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_ebd1a6d5-0918-4dc2-b24f-26d58f97fca8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_f8df9848-528c-4eae-b1b0-964117e8f372" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_ebd1a6d5-0918-4dc2-b24f-26d58f97fca8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8117cb8c-ae81-4d11-a413-a232c0c5cb5e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_ebd1a6d5-0918-4dc2-b24f-26d58f97fca8" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8117cb8c-ae81-4d11-a413-a232c0c5cb5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8117cb8c-ae81-4d11-a413-a232c0c5cb5e_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8117cb8c-ae81-4d11-a413-a232c0c5cb5e" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8117cb8c-ae81-4d11-a413-a232c0c5cb5e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f94d6e85-1443-4e50-8ad6-f6489babcf3b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8117cb8c-ae81-4d11-a413-a232c0c5cb5e" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f94d6e85-1443-4e50-8ad6-f6489babcf3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_cb835349-b8c4-4858-a53b-f282d89d478c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f94d6e85-1443-4e50-8ad6-f6489babcf3b" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_cb835349-b8c4-4858-a53b-f282d89d478c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_90579aaf-6cba-4c79-8294-8f376a7b7665" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f94d6e85-1443-4e50-8ad6-f6489babcf3b" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_90579aaf-6cba-4c79-8294-8f376a7b7665" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_a898f052-2de0-4b51-9d0f-19d1fbb3b6ab" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f94d6e85-1443-4e50-8ad6-f6489babcf3b" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_a898f052-2de0-4b51-9d0f-19d1fbb3b6ab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_bf587d83-ea36-4ca4-bb26-6e8701184cbb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_ebd1a6d5-0918-4dc2-b24f-26d58f97fca8" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_bf587d83-ea36-4ca4-bb26-6e8701184cbb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_bf587d83-ea36-4ca4-bb26-6e8701184cbb_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_bf587d83-ea36-4ca4-bb26-6e8701184cbb" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_bf587d83-ea36-4ca4-bb26-6e8701184cbb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_05944cf1-7ae8-4f18-8339-57385f8bbdcd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_bf587d83-ea36-4ca4-bb26-6e8701184cbb" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_05944cf1-7ae8-4f18-8339-57385f8bbdcd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_6dad1a58-49a6-459d-b55f-ee22c02b1581" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_05944cf1-7ae8-4f18-8339-57385f8bbdcd" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_6dad1a58-49a6-459d-b55f-ee22c02b1581" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_e76c5a39-bf39-43a5-a79e-2f818e68d37f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_ebd1a6d5-0918-4dc2-b24f-26d58f97fca8" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_e76c5a39-bf39-43a5-a79e-2f818e68d37f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_e76c5a39-bf39-43a5-a79e-2f818e68d37f_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_e76c5a39-bf39-43a5-a79e-2f818e68d37f" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_e76c5a39-bf39-43a5-a79e-2f818e68d37f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_b76c5ecc-dec0-41d2-80e7-4624167a2db2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_e76c5a39-bf39-43a5-a79e-2f818e68d37f" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_b76c5ecc-dec0-41d2-80e7-4624167a2db2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_f367fd94-2ad2-48ea-b9a5-0f194e4748b8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_b76c5ecc-dec0-41d2-80e7-4624167a2db2" xlink:to="loc_us-gaap_InterestRateSwapMember_f367fd94-2ad2-48ea-b9a5-0f194e4748b8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_4e4fa827-9bb6-4381-a434-2763b02422c8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_ebd1a6d5-0918-4dc2-b24f-26d58f97fca8" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_4e4fa827-9bb6-4381-a434-2763b02422c8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_4e4fa827-9bb6-4381-a434-2763b02422c8_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_4e4fa827-9bb6-4381-a434-2763b02422c8" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_4e4fa827-9bb6-4381-a434-2763b02422c8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_dc60189c-fcab-4334-89f5-20d1eda5ab21" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_4e4fa827-9bb6-4381-a434-2763b02422c8" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_dc60189c-fcab-4334-89f5-20d1eda5ab21" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_cd93395e-f1eb-42e6-ae89-b3a2ccc83e69" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_dc60189c-fcab-4334-89f5-20d1eda5ab21" xlink:to="loc_us-gaap_MoneyMarketFundsMember_cd93395e-f1eb-42e6-ae89-b3a2ccc83e69" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/CommitmentsandContingenciesDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#CommitmentsandContingenciesDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/CommitmentsandContingenciesDetails" xlink:type="extended" id="ia536df95245e45ffb9a2667036bfd7ef_CommitmentsandContingenciesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentLineItems_3e4c67ff-7103-48b9-8cb6-6b5b905950e1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermPurchaseCommitmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentAmount_48ac4780-d879-4aea-a8db-68226996decb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermPurchaseCommitmentAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_3e4c67ff-7103-48b9-8cb6-6b5b905950e1" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentAmount_48ac4780-d879-4aea-a8db-68226996decb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentTable_e6e4b191-4012-407d-9d45-da23062f34ea" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermPurchaseCommitmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_3e4c67ff-7103-48b9-8cb6-6b5b905950e1" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentTable_e6e4b191-4012-407d-9d45-da23062f34ea" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis_74291e01-5976-4cef-8ce0-5648e6ed53e2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_e6e4b191-4012-407d-9d45-da23062f34ea" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis_74291e01-5976-4cef-8ce0-5648e6ed53e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain_74291e01-5976-4cef-8ce0-5648e6ed53e2_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis_74291e01-5976-4cef-8ce0-5648e6ed53e2" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain_74291e01-5976-4cef-8ce0-5648e6ed53e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain_b370a566-207f-45d2-8f0b-5fc4efa643df" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis_74291e01-5976-4cef-8ce0-5648e6ed53e2" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain_b370a566-207f-45d2-8f0b-5fc4efa643df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_HostedSoftwareSolutionsMember_8e5366f2-2294-434c-8aaa-4f7a67fbf72c" xlink:href="bsy-20210630.xsd#bsy_HostedSoftwareSolutionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain_b370a566-207f-45d2-8f0b-5fc4efa643df" xlink:to="loc_bsy_HostedSoftwareSolutionsMember_8e5366f2-2294-434c-8aaa-4f7a67fbf72c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/GeographicDataDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#GeographicDataDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/GeographicDataDetails" xlink:type="extended" id="i05f4db3d00994d8188a0c3748631fc04_GeographicDataDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_5e965087-904d-4cdc-8307-19331e4b5b2b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncurrentAssets_40d1c457-2a92-4587-b132-e04b24eacdf0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_5e965087-904d-4cdc-8307-19331e4b5b2b" xlink:to="loc_us-gaap_NoncurrentAssets_40d1c457-2a92-4587-b132-e04b24eacdf0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_9674dc35-0ad0-4fdb-85a7-eb6607648b47" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_5e965087-904d-4cdc-8307-19331e4b5b2b" xlink:to="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_9674dc35-0ad0-4fdb-85a7-eb6607648b47" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_c0dac82f-2c4d-4b9d-9ed8-7e389548945e" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_9674dc35-0ad0-4fdb-85a7-eb6607648b47" xlink:to="loc_srt_StatementGeographicalAxis_c0dac82f-2c4d-4b9d-9ed8-7e389548945e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_c0dac82f-2c4d-4b9d-9ed8-7e389548945e_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_c0dac82f-2c4d-4b9d-9ed8-7e389548945e" xlink:to="loc_srt_SegmentGeographicalDomain_c0dac82f-2c4d-4b9d-9ed8-7e389548945e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_da78c90c-1b7f-4cfa-ae38-6d257e28bfc9" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_c0dac82f-2c4d-4b9d-9ed8-7e389548945e" xlink:to="loc_srt_SegmentGeographicalDomain_da78c90c-1b7f-4cfa-ae38-6d257e28bfc9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_UnitedStatesCanadaLatinAmericaAndCaribbeanMember_0850c21c-b676-42e2-ab93-a176c7e3861e" xlink:href="bsy-20210630.xsd#bsy_UnitedStatesCanadaLatinAmericaAndCaribbeanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_da78c90c-1b7f-4cfa-ae38-6d257e28bfc9" xlink:to="loc_bsy_UnitedStatesCanadaLatinAmericaAndCaribbeanMember_0850c21c-b676-42e2-ab93-a176c7e3861e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EMEAMember_67389dbf-e35d-4c9c-b389-4b33fcef89d4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EMEAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_da78c90c-1b7f-4cfa-ae38-6d257e28bfc9" xlink:to="loc_us-gaap_EMEAMember_67389dbf-e35d-4c9c-b389-4b33fcef89d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AsiaPacificMember_1cf5d834-43ba-48f8-b44c-d85f30b57cf6" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_AsiaPacificMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_da78c90c-1b7f-4cfa-ae38-6d257e28bfc9" xlink:to="loc_srt_AsiaPacificMember_1cf5d834-43ba-48f8-b44c-d85f30b57cf6" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/RealignmentCostsNarrativeDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#RealignmentCostsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/RealignmentCostsNarrativeDetails" xlink:type="extended" id="ibef60e95953e48fe8c1090b5808bfba7_RealignmentCostsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_2b1972da-2217-4575-bdb7-d14db0496766" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_67a7435a-0cde-4611-8af7-402cacd8dee8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_2b1972da-2217-4575-bdb7-d14db0496766" xlink:to="loc_us-gaap_RestructuringCharges_67a7435a-0cde-4611-8af7-402cacd8dee8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_d98872b3-56dd-43be-bdab-a7f2f269aeea" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_2b1972da-2217-4575-bdb7-d14db0496766" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_d98872b3-56dd-43be-bdab-a7f2f269aeea" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_e833f9d9-a185-4dad-9416-914367915610" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_d98872b3-56dd-43be-bdab-a7f2f269aeea" xlink:to="loc_us-gaap_RestructuringPlanAxis_e833f9d9-a185-4dad-9416-914367915610" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_e833f9d9-a185-4dad-9416-914367915610_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_e833f9d9-a185-4dad-9416-914367915610" xlink:to="loc_us-gaap_RestructuringPlanDomain_e833f9d9-a185-4dad-9416-914367915610_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_bda3d245-a5e6-4408-a4df-9e82f6e99782" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_e833f9d9-a185-4dad-9416-914367915610" xlink:to="loc_us-gaap_RestructuringPlanDomain_bda3d245-a5e6-4408-a4df-9e82f6e99782" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentyStrategicRealignmentProgramMember_e289f300-2248-40f0-a0ed-47d8b911bec9" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentyStrategicRealignmentProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_bda3d245-a5e6-4408-a4df-9e82f6e99782" xlink:to="loc_bsy_TwoThousandTwentyStrategicRealignmentProgramMember_e289f300-2248-40f0-a0ed-47d8b911bec9" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/EarningsPerShareScheduleofBasicandDilutedEPSDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#EarningsPerShareScheduleofBasicandDilutedEPSDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/EarningsPerShareScheduleofBasicandDilutedEPSDetails" xlink:type="extended" id="i3309baa3d5a0442a8b3e17a98d685872_EarningsPerShareScheduleofBasicandDilutedEPSDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDilutedLineItems_cfbebf41-40f3-44ed-89a2-860f4a17cca1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EarningsPerShareDilutedLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_NumeratorAbstract_553b5f91-7272-4d66-b342-8a9f5ddc0a18" xlink:href="bsy-20210630.xsd#bsy_NumeratorAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareDilutedLineItems_cfbebf41-40f3-44ed-89a2-860f4a17cca1" xlink:to="loc_bsy_NumeratorAbstract_553b5f91-7272-4d66-b342-8a9f5ddc0a18" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_1c4714c4-2c92-407b-9e80-9c608a7fe689" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_NumeratorAbstract_553b5f91-7272-4d66-b342-8a9f5ddc0a18" xlink:to="loc_us-gaap_NetIncomeLoss_1c4714c4-2c92-407b-9e80-9c608a7fe689" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesBasic_1877d6c8-017a-4453-9985-86659c4f6d95" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_NumeratorAbstract_553b5f91-7272-4d66-b342-8a9f5ddc0a18" xlink:to="loc_us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesBasic_1877d6c8-017a-4453-9985-86659c4f6d95" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_08f7fa85-9520-429f-a1c9-5d5732fecf95" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_NumeratorAbstract_553b5f91-7272-4d66-b342-8a9f5ddc0a18" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_08f7fa85-9520-429f-a1c9-5d5732fecf95" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestOnConvertibleDebtNetOfTax_1ccd1b44-95f2-41d9-b6f4-ff7872aded0c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestOnConvertibleDebtNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_NumeratorAbstract_553b5f91-7272-4d66-b342-8a9f5ddc0a18" xlink:to="loc_us-gaap_InterestOnConvertibleDebtNetOfTax_1ccd1b44-95f2-41d9-b6f4-ff7872aded0c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_ea1235f8-0cd2-4ea0-ad11-700133b9fcdf" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_NumeratorAbstract_553b5f91-7272-4d66-b342-8a9f5ddc0a18" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_ea1235f8-0cd2-4ea0-ad11-700133b9fcdf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_DenominatorAbstract_cd90ed50-2a8e-4dbf-8489-4e9398163559" xlink:href="bsy-20210630.xsd#bsy_DenominatorAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareDilutedLineItems_cfbebf41-40f3-44ed-89a2-860f4a17cca1" xlink:to="loc_bsy_DenominatorAbstract_cd90ed50-2a8e-4dbf-8489-4e9398163559" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_e56f05fc-136f-4c04-98e8-3f3cc8effae6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_DenominatorAbstract_cd90ed50-2a8e-4dbf-8489-4e9398163559" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_e56f05fc-136f-4c04-98e8-3f3cc8effae6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment_31689f27-5471-4197-b2e1-22a360127df7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_DenominatorAbstract_cd90ed50-2a8e-4dbf-8489-4e9398163559" xlink:to="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment_31689f27-5471-4197-b2e1-22a360127df7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_9244bdd5-3686-4363-88c4-8a5df0760726" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_DenominatorAbstract_cd90ed50-2a8e-4dbf-8489-4e9398163559" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_9244bdd5-3686-4363-88c4-8a5df0760726" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities_5aad0b2d-be02-4782-9821-0b317502b985" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_DenominatorAbstract_cd90ed50-2a8e-4dbf-8489-4e9398163559" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities_5aad0b2d-be02-4782-9821-0b317502b985" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_bc007d04-2fa5-4342-9e80-b2e0664cf743" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_bsy_DenominatorAbstract_cd90ed50-2a8e-4dbf-8489-4e9398163559" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_bc007d04-2fa5-4342-9e80-b2e0664cf743" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_ab5712ea-a7d6-4e9c-bdd4-31f7325a8eac" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareDilutedLineItems_cfbebf41-40f3-44ed-89a2-860f4a17cca1" xlink:to="loc_us-gaap_EarningsPerShareBasic_ab5712ea-a7d6-4e9c-bdd4-31f7325a8eac" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_d091b52a-7c40-4ba2-9502-07354b2e76b7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareDilutedLineItems_cfbebf41-40f3-44ed-89a2-860f4a17cca1" xlink:to="loc_us-gaap_EarningsPerShareDiluted_d091b52a-7c40-4ba2-9502-07354b2e76b7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable_1f7489d3-8b91-4117-954c-79b93e747c0b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EarningsPerShareDilutedLineItems_cfbebf41-40f3-44ed-89a2-860f4a17cca1" xlink:to="loc_us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable_1f7489d3-8b91-4117-954c-79b93e747c0b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_caa77957-0996-4262-b312-04c5600caffa" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable_1f7489d3-8b91-4117-954c-79b93e747c0b" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_caa77957-0996-4262-b312-04c5600caffa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_caa77957-0996-4262-b312-04c5600caffa_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_caa77957-0996-4262-b312-04c5600caffa" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_caa77957-0996-4262-b312-04c5600caffa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_efa5cc78-1b26-4f68-98ff-798cb27c63b6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_caa77957-0996-4262-b312-04c5600caffa" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_efa5cc78-1b26-4f68-98ff-798cb27c63b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_a54c7a7d-005e-40fc-8b8d-554eea9389bc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_efa5cc78-1b26-4f68-98ff-798cb27c63b6" xlink:to="loc_us-gaap_ConvertibleDebtMember_a54c7a7d-005e-40fc-8b8d-554eea9389bc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_a1ddc89d-9873-425a-b434-152be8524796" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable_1f7489d3-8b91-4117-954c-79b93e747c0b" xlink:to="loc_us-gaap_DebtInstrumentAxis_a1ddc89d-9873-425a-b434-152be8524796" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_a1ddc89d-9873-425a-b434-152be8524796_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_a1ddc89d-9873-425a-b434-152be8524796" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_a1ddc89d-9873-425a-b434-152be8524796_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_d0f50663-0148-4ea6-9fc9-689f403b0b15" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_a1ddc89d-9873-425a-b434-152be8524796" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_d0f50663-0148-4ea6-9fc9-689f403b0b15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_TwoThousandTwentySixNotesMember_e11bb3cf-4891-458c-a7d9-348c3f7c058e" xlink:href="bsy-20210630.xsd#bsy_TwoThousandTwentySixNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d0f50663-0148-4ea6-9fc9-689f403b0b15" xlink:to="loc_bsy_TwoThousandTwentySixNotesMember_e11bb3cf-4891-458c-a7d9-348c3f7c058e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bentley.com/role/EarningsPerShareScheduleofAntidilutiveSecuritiesExcludedfromComputationofEarningsPerShareDetails" xlink:type="simple" xlink:href="bsy-20210630.xsd#EarningsPerShareScheduleofAntidilutiveSecuritiesExcludedfromComputationofEarningsPerShareDetails"/>
  <link:definitionLink xlink:role="http://www.bentley.com/role/EarningsPerShareScheduleofAntidilutiveSecuritiesExcludedfromComputationofEarningsPerShareDetails" xlink:type="extended" id="iacc971e0d2d74bf6a07becaa6a21a776_EarningsPerShareScheduleofAntidilutiveSecuritiesExcludedfromComputationofEarningsPerShareDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_5e420672-1c82-4e04-84c6-1f12b606cfe1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_65a5eaa3-e29e-4f15-9b9f-48e478882a4b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_5e420672-1c82-4e04-84c6-1f12b606cfe1" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_65a5eaa3-e29e-4f15-9b9f-48e478882a4b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_2418d539-8686-48d2-a735-d27a82f98df9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_5e420672-1c82-4e04-84c6-1f12b606cfe1" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_2418d539-8686-48d2-a735-d27a82f98df9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_8105ff39-4e49-4ef0-bd89-746ee845895c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_2418d539-8686-48d2-a735-d27a82f98df9" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_8105ff39-4e49-4ef0-bd89-746ee845895c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_8105ff39-4e49-4ef0-bd89-746ee845895c_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_8105ff39-4e49-4ef0-bd89-746ee845895c" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_8105ff39-4e49-4ef0-bd89-746ee845895c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9df565f6-9222-4c67-9e8d-69141734d2b9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_8105ff39-4e49-4ef0-bd89-746ee845895c" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9df565f6-9222-4c67-9e8d-69141734d2b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bsy_StockOptionsRestrictedStockAndRestrictedStockUnitsRSUsMember_3b820e58-fb76-4d13-a19d-44eeba7d0430" xlink:href="bsy-20210630.xsd#bsy_StockOptionsRestrictedStockAndRestrictedStockUnitsRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9df565f6-9222-4c67-9e8d-69141734d2b9" xlink:to="loc_bsy_StockOptionsRestrictedStockAndRestrictedStockUnitsRSUsMember_3b820e58-fb76-4d13-a19d-44eeba7d0430" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
