AimTo examine assumptions about public–private partnership (PPP) activities and their role in improving public procurement of primary healthcare surgeries.BackgroundPPPs were developed to improve the quality of care and patient satisfaction. However, evidence of their effectiveness in delivering health benefits is limited.MethodsA qualitative study design was employed. A total of 25 interviews with public sector staff (n=23) and private sector managers (n=2) were conducted to understand their interpretations of assumptions in the activities of private investors and service contractors participating in Local Improvement Finance Trust (LIFT) partnerships. Realist evaluation principles were applied in the data analysis to interpret the findings.ResultsSix thematic areas of assumed health benefits were identified: (i) quality improvement; (ii) improved risk management; (iii) reduced procurement costs; (iv) increased efficiency; (v) community involvement; and (vi) sustainable investment. Primary Care Trusts that chose to procure their surgeries through LIFT were expected to support its implementation by providing an environment conducive for the private participants to achieve these benefits. Private participant activities were found to be based on a range of explicit and tacit assumptions perceived helpful in achieving government objectives for LIFT.ConclusionThe success of PPPs depended upon private participants’ (i) capacity to assess how PPP assumptions added value to their activities, (ii) effectiveness in interpreting assumptions in their expected activities, and (iii) preparedness to align their business principles to government objectives for PPPs. They risked missing some of the expected benefits because of some factors constraining realization of the assumptions. The ways in which private participants preferred to carry out their activities also influenced the extent to which expected benefits were achieved. Giving more discretion to public than private participants over critical decisions may help in ensuring that assumptions in PPP activities result in outcomes that match the anticipated health benefits.