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

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2022 Workiva-->
<!--r:fd136a20-78cc-4f19-bffb-684d916e7a8d,g:5a31d2f8-e7e3-49c1-a560-d5c816005ce9-->
<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.brandywinerealty.com/role/DocumentandEntityInformationDocument" xlink:type="simple" xlink:href="bdn-20221020.xsd#DocumentandEntityInformationDocument"/>
  <link:definitionLink xlink:role="http://www.brandywinerealty.com/role/DocumentandEntityInformationDocument" xlink:type="extended" id="id5bd31375e4748108be4ef746c62df6b_DocumentandEntityInformationDocument">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_b1bdaa72-f3df-42a6-a985-df653abd054e" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_DocumentType_b1bdaa72-f3df-42a6-a985-df653abd054e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_572ecabe-28b6-4aa1-bdba-b6e9dc279d10" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_DocumentPeriodEndDate_572ecabe-28b6-4aa1-bdba-b6e9dc279d10" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_921469b9-a818-4bd1-ae35-ea3cf39364b3" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_EntityRegistrantName_921469b9-a818-4bd1-ae35-ea3cf39364b3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_3a3eeb60-763f-43c0-9812-64b819681f3f" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_EntityIncorporationStateCountryCode_3a3eeb60-763f-43c0-9812-64b819681f3f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_523ae0bf-0b85-4ada-b627-54972c879d06" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_EntityFileNumber_523ae0bf-0b85-4ada-b627-54972c879d06" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_9ccecad6-e816-46c3-a026-c0aa63662838" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_EntityTaxIdentificationNumber_9ccecad6-e816-46c3-a026-c0aa63662838" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_5715f2e2-5392-4065-94aa-32744476876d" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_EntityAddressAddressLine1_5715f2e2-5392-4065-94aa-32744476876d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_9907c035-ec02-45d0-9a9d-af53f98ccab4" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_EntityAddressAddressLine2_9907c035-ec02-45d0-9a9d-af53f98ccab4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_3585e8a7-296d-43fa-bf59-ce3fff758b07" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_EntityAddressCityOrTown_3585e8a7-296d-43fa-bf59-ce3fff758b07" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_2d62659a-4a3f-4e48-88fb-f0cbe9d39a37" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_EntityAddressStateOrProvince_2d62659a-4a3f-4e48-88fb-f0cbe9d39a37" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_096dc40a-19a4-438a-b8fb-3fb6363789d2" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_EntityAddressPostalZipCode_096dc40a-19a4-438a-b8fb-3fb6363789d2" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_eea0921e-1fb5-4319-b1f4-034504e378f1" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_CityAreaCode_eea0921e-1fb5-4319-b1f4-034504e378f1" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_3a0c2e76-6b23-4ecc-8d48-4e8ef8de8a3d" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_LocalPhoneNumber_3a0c2e76-6b23-4ecc-8d48-4e8ef8de8a3d" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_716b4480-5430-4e2b-828e-5d4f82731ba8" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_WrittenCommunications_716b4480-5430-4e2b-828e-5d4f82731ba8" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_d8aca7e9-af87-496d-bd51-6918f0674a99" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_SolicitingMaterial_d8aca7e9-af87-496d-bd51-6918f0674a99" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_5940bf7d-f91c-4cf4-99c0-f4d791071dd6" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_PreCommencementTenderOffer_5940bf7d-f91c-4cf4-99c0-f4d791071dd6" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_78614736-18da-4be5-bd59-e158553e65ba" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_78614736-18da-4be5-bd59-e158553e65ba" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_8a25949b-0bfa-4e78-a6d8-38f5a1227627" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_Security12bTitle_8a25949b-0bfa-4e78-a6d8-38f5a1227627" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_d027acf8-4a0d-4033-9561-eabc5098298e" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_TradingSymbol_d027acf8-4a0d-4033-9561-eabc5098298e" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_478ce02f-e848-4347-8d8d-7ed593a02ab7" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_SecurityExchangeName_478ce02f-e848-4347-8d8d-7ed593a02ab7" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_abf9380f-3ff3-4339-8857-2c28f0477d92" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_EntityEmergingGrowthCompany_abf9380f-3ff3-4339-8857-2c28f0477d92" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_76f80840-d06c-4f9c-b1a9-b5c5a33005e1" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_EntityCentralIndexKey_76f80840-d06c-4f9c-b1a9-b5c5a33005e1" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_1e482053-3650-4320-a1c8-baf4d20f83a1" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_AmendmentFlag_1e482053-3650-4320-a1c8-baf4d20f83a1" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_3bcbc955-283a-4553-be2c-a614675b851a" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_7ed6f8c8-ee4a-424c-a7a4-f4df243dfe7f" xlink:to="loc_dei_EntitiesTable_3bcbc955-283a-4553-be2c-a614675b851a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_65d07ce0-a927-44b2-8e09-27803d1700ed" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_3bcbc955-283a-4553-be2c-a614675b851a" xlink:to="loc_dei_LegalEntityAxis_65d07ce0-a927-44b2-8e09-27803d1700ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_65d07ce0-a927-44b2-8e09-27803d1700ed_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_65d07ce0-a927-44b2-8e09-27803d1700ed" xlink:to="loc_dei_EntityDomain_65d07ce0-a927-44b2-8e09-27803d1700ed_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_594b49f3-f830-4acb-b733-ec92af59898d" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_65d07ce0-a927-44b2-8e09-27803d1700ed" xlink:to="loc_dei_EntityDomain_594b49f3-f830-4acb-b733-ec92af59898d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_bdn_BrandywineOperatingPartnershipL.P.Member_1b8a223b-2e61-4801-bdaa-0dc56c2b3e0c" xlink:href="bdn-20221020.xsd#bdn_BrandywineOperatingPartnershipL.P.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_594b49f3-f830-4acb-b733-ec92af59898d" xlink:to="loc_bdn_BrandywineOperatingPartnershipL.P.Member_1b8a223b-2e61-4801-bdaa-0dc56c2b3e0c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressesAddressTypeAxis_42c24531-817b-4bec-af0c-358d451075a1" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityAddressesAddressTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_3bcbc955-283a-4553-be2c-a614675b851a" xlink:to="loc_dei_EntityAddressesAddressTypeAxis_42c24531-817b-4bec-af0c-358d451075a1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AddressTypeDomain_42c24531-817b-4bec-af0c-358d451075a1_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_AddressTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_EntityAddressesAddressTypeAxis_42c24531-817b-4bec-af0c-358d451075a1" xlink:to="loc_dei_AddressTypeDomain_42c24531-817b-4bec-af0c-358d451075a1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AddressTypeDomain_be8f93a5-2e1b-4f5a-ad76-381e48131e4f" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_AddressTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_EntityAddressesAddressTypeAxis_42c24531-817b-4bec-af0c-358d451075a1" xlink:to="loc_dei_AddressTypeDomain_be8f93a5-2e1b-4f5a-ad76-381e48131e4f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_FormerAddressMember_4a138bb6-b5cf-4a65-977a-c053518988c3" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_FormerAddressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_AddressTypeDomain_be8f93a5-2e1b-4f5a-ad76-381e48131e4f" xlink:to="loc_dei_FormerAddressMember_4a138bb6-b5cf-4a65-977a-c053518988c3" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
