IntroductionEngaging communities and intended beneficiaries at various stages of health research is a recommended practice. The contribution of community engagement to non-communicable disease research in low- and middle-income countries has not yet been extensively studied or synthesised. This protocol describes the steps towards generating an understanding of community engagement in the context of non-communicable disease research, prevention and health promotion using a realist review approach. A realist lens enables a rich explanatory approach to causation while capturing complexity, and an openness to multiple outcomes, including unintended consequences. The review will thus develop an understanding of community engagement without assuming that such practices result in more ethical research or effective interventions.Methods and analysisWe propose a realist approach aiming to examine how, why, under what circumstances and for whom community engagement works or does not work. The iterative review steps include clarifying the review scope; searching for evidence; appraising studies and extracting data; synthesising evidence and drawing conclusions; and disseminating, implementing and evaluating the findings. Principles of meta-narrative review (pragmatism, pluralism, historicity, contestation, reflexivity and peer review) are employed to ensure practicable and contextualised review outputs. The proposed review will draw on theoretical and empirical literature beyond specific diseases or settings, but with a focus on informing non-communicable disease research and interventions in low- and middle-income countries. The synthesis of existing literature will be complemented by qualitative realist interviews and stakeholder consultation. Through drawing on multiple types of evidence and input from both experts and intended beneficiaries, the review will provide critical and pragmatic insights for research and community engagement in low- and middle-income countries.Ethics and disseminationEthical approval has been obtained from the University of the Witwatersrand. Dissemination will include traditional academic channels, institutional communications, social media and discussions with a wide range of stakeholders.