Introduction As the world responds to COVID-19 and aims for the Sustainable Development Goals, the potential for primary healthcare (PHC) is substantial, although the trends and effectiveness of PHC expenditure are unknown. We estimate PHC expenditure for each low-income and middle-income country between 2000 and 2017 and test which health outputs and outcomes were associated with PHC expenditure. Methods We used three data sources to estimate PHC expenditures: recently published health expenditure estimates for each low-income and middle-income country, which were constructed using 1662 country-reported National Health Accounts; proprietary data from IQVIA to estimate expenditure of prescribed pharmaceuticals for PHC; and household surveys and costing estimates to estimate inpatient vaginal delivery expenditures. We employed regression analyses to measure the association between PHC expenditures and 15 health outcomes and intermediate health outputs. Results PHC expenditures in low-income and middle-income countries increased between 2000 and 2017, from 41percapita(95%uncertaintyinterval 33–49)to 90 (73– 105). Expenditures for low-income countries plateaued since 2014 at 17percapita( 15–19).Asnationalincomeincreased,theproportionofhealthexpendituresonPHCgenerallydecrease;however,thefractionofPHCexpendituresspentviaambulatorycareprovidersgrew.IncreasesinthefractionofhealthexpendituresonPHCwasassociatedwithlowermaternalmortalityrate(pvalue≤0.001),improvedcoverageofantenatalcarevisits(pvalue≤0.001),measlesvaccination(pvalue≤0.001)andanincreaseintheHealthAccessandQualityindex(pvalue≤0.05).PHCexpenditurewasnotsystematicallyassociatedwithall-agemortality,communicableandnon-communicabledisease(NCD)burden.ConclusionPHCexpenditureswereassociatedwithmaternalandchildhealthbutwerenotassociatedwithreductioninhealthburdenforotherkeycausesofdisability,suchasNCDs.Tocombatchangingdiseaseburdens,policy-makersandhealthprofessionalsneedtoadaptprimaryhealthcaretoensurecontinuedimpactonemerginghealthchallenges.