Community engagement is central to national strategies for promoting health, yet there have been few attempts to systematically review the evidence on the impact of initiatives that aim to engage communities. This rapid review fills this gap by exploring the population impact of initiatives which sought to address social determinants of health. It took a novel approach to synthesizing a sample of the enormous UK literature on community engagement. The synthesis found no evidence of positive impacts on population health or the quality of services, but initiatives did have positive impacts on housing, crime, social capital and community empowerment. Methodological developments are needed to enable studies of complex social interventions to provide robust evidence of population impact in relation to community engagement.