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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2025 Workiva-->
<!--r:08dcc400-7a49-407f-ab56-7a90f58c831a,g:6f90a554-6036-4199-a828-6951a25a242f-->
<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.blaize.com/role/Cover" xlink:type="simple" xlink:href="blz-20251203.xsd#Cover"/>
  <link:definitionLink xlink:role="http://www.blaize.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_fde1db8b-c62c-4eeb-94d3-e5046cd473a5" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_DocumentInformationTable_fde1db8b-c62c-4eeb-94d3-e5046cd473a5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_89dadb4b-0616-41c9-aeee-fcf5a87fa1c8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_fde1db8b-c62c-4eeb-94d3-e5046cd473a5" xlink:to="loc_us-gaap_StatementClassOfStockAxis_89dadb4b-0616-41c9-aeee-fcf5a87fa1c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_89dadb4b-0616-41c9-aeee-fcf5a87fa1c8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_89dadb4b-0616-41c9-aeee-fcf5a87fa1c8" xlink:to="loc_us-gaap_ClassOfStockDomain_89dadb4b-0616-41c9-aeee-fcf5a87fa1c8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_dadcc6ea-6bba-408c-8cd0-31c054ae2c5c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_89dadb4b-0616-41c9-aeee-fcf5a87fa1c8" xlink:to="loc_us-gaap_ClassOfStockDomain_dadcc6ea-6bba-408c-8cd0-31c054ae2c5c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_9f258b76-be30-441c-ae11-f85fb146be44" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_dadcc6ea-6bba-408c-8cd0-31c054ae2c5c" xlink:to="loc_us-gaap_CommonStockMember_9f258b76-be30-441c-ae11-f85fb146be44" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_f1f22d6a-1f2b-4669-a532-ff61175bb1fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_dadcc6ea-6bba-408c-8cd0-31c054ae2c5c" xlink:to="loc_us-gaap_WarrantMember_f1f22d6a-1f2b-4669-a532-ff61175bb1fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_77cd1d6a-c22c-43bf-9dd3-e92fdb7a4284" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_DocumentType_77cd1d6a-c22c-43bf-9dd3-e92fdb7a4284" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_2282a030-03a4-41ef-a502-e89504d2ab7a" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_DocumentPeriodEndDate_2282a030-03a4-41ef-a502-e89504d2ab7a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_764ab8fd-7622-4940-b260-4d6bf9737ade" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_EntityRegistrantName_764ab8fd-7622-4940-b260-4d6bf9737ade" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_78a4bdc1-dba2-4e4d-87df-3ba0e6cceb18" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_EntityIncorporationStateCountryCode_78a4bdc1-dba2-4e4d-87df-3ba0e6cceb18" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_23e48019-fa86-44fd-b50e-e06afe9be223" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_EntityFileNumber_23e48019-fa86-44fd-b50e-e06afe9be223" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_a9205419-5e5e-4ce0-83cc-387c37382117" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_EntityTaxIdentificationNumber_a9205419-5e5e-4ce0-83cc-387c37382117" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_56774212-63bf-4a1c-9c2a-814da5339ee2" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_EntityAddressAddressLine1_56774212-63bf-4a1c-9c2a-814da5339ee2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_d464f944-b081-46a4-9782-f224f2d94352" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_EntityAddressAddressLine2_d464f944-b081-46a4-9782-f224f2d94352" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_29e8897e-3b1c-4781-95f9-c92e34bf5a52" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_EntityAddressCityOrTown_29e8897e-3b1c-4781-95f9-c92e34bf5a52" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_733a0294-29f4-4b06-aa3b-547a5c92865b" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_EntityAddressStateOrProvince_733a0294-29f4-4b06-aa3b-547a5c92865b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_1d5701f8-66bd-47c7-a73b-ff75c02c6021" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_EntityAddressPostalZipCode_1d5701f8-66bd-47c7-a73b-ff75c02c6021" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_70ecb715-6208-464a-928e-f741168cecaf" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_CityAreaCode_70ecb715-6208-464a-928e-f741168cecaf" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_52b79f5f-cbbb-4af4-94f1-4af6d9ef7485" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_LocalPhoneNumber_52b79f5f-cbbb-4af4-94f1-4af6d9ef7485" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_87133cc7-be33-4231-b31c-26a0c3d51016" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_WrittenCommunications_87133cc7-be33-4231-b31c-26a0c3d51016" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_f63b9bba-389a-4bf5-8e66-9dc90089b2d2" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_SolicitingMaterial_f63b9bba-389a-4bf5-8e66-9dc90089b2d2" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_aa84f526-d8df-4df4-ae43-96ce086bff71" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_PreCommencementTenderOffer_aa84f526-d8df-4df4-ae43-96ce086bff71" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_332aa336-0c5b-42ae-b6bf-51546b6fd8dc" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_332aa336-0c5b-42ae-b6bf-51546b6fd8dc" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_5b998b1c-9469-4a19-8cf2-bd26fc7cc86b" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_Security12bTitle_5b998b1c-9469-4a19-8cf2-bd26fc7cc86b" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_9866389f-4eba-4825-bd95-5857204f1940" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_TradingSymbol_9866389f-4eba-4825-bd95-5857204f1940" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_cdae37a5-e4d6-44e7-bd02-1da0f1919fa4" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_SecurityExchangeName_cdae37a5-e4d6-44e7-bd02-1da0f1919fa4" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_199599c0-9068-4f86-85be-7c733becb4de" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_EntityEmergingGrowthCompany_199599c0-9068-4f86-85be-7c733becb4de" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityExTransitionPeriod_2cab43aa-d053-4a82-bdb1-de3d8b428098" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityExTransitionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_EntityExTransitionPeriod_2cab43aa-d053-4a82-bdb1-de3d8b428098" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_3772a2b7-fe2d-4798-b90f-264d74209881" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_EntityCentralIndexKey_3772a2b7-fe2d-4798-b90f-264d74209881" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_e8ed0a3b-abfa-4e7a-92f8-46344a5e9b0c" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_08e94d00-80d3-4a64-8877-d8226e1e4128" xlink:to="loc_dei_AmendmentFlag_e8ed0a3b-abfa-4e7a-92f8-46344a5e9b0c" xlink:type="arc" order="23"/>
  </link:definitionLink>
</link:linkbase>
