Background Greater investment in primary care yields better population health outcomes. However, in the past decade general practice (GP) funding has reduced, while general practitioner workload has risen and secondary care funding has increased. To date, the impact of broader aspects of GP funding has not been examined. Using newly released GP financial data, we aimed to explore the association between greater investment in primary care and secondary care usage and costs applied at a national level in England. Methods We constructed linear regression models to explore the association between practice funding for essential services and quality and outcomes framework (QOF) achievement, secondary care usage (accident and emergency [A&E] attendance, emergency admission, and outpatient attendance rates per 1000 registered patients), and patient satisfaction, adjusted for practice and demographic variables. We then conducted financial modelling to predict the impact of a hypothetical 10% funding increase on secondary care costs, for which we used standard cost estimates. Findings We analysed 7767 practices in England. Mean funding per patient was £79·81 (95% CI 67·01–100·67). Funding was lower in General Medical Services (GMS) practices, which hold national contracts, than in Personal Medical Services practices, which have local contracts (£76·00 [66·52–89·20] vs 84·43 [66·68–107·09]). In GMS practices, greater funding was significantly associated with lower emergency admissions (regression coefficient β=–0·22), lower A&E attendances (−1·04), and higher patient satisfaction (overall satisfaction 0·4). We found no significant association with outpatient attendance or QOF performance. In our financial model, a 10% increase in primary care funding would create a return on investment of 78% in GMS practices overall and up to 110% in GMS practices receiving funding above the national capitation formula. Interpretation GMS practices with higher levels of funding had lower secondary care usage and higher patient satisfaction. The lack of association between funding and QOF achievement might be attributable to the different funding stream and incentives for QOF. Our findings support the case for greater investment in primary care where the value of investment is over and above the national capitation formula. Funding National Institute for Health Research.