© 2020 The Author(s). Background: Within our inquiry into the implementation of breastfeeding policy in Malawi, Care Groups have been mentioned as a means to improve maternal and child health and nutrition outcomes. The 'Care Group model' is an approach primarily used in international development settings, whereby social and behaviour changes are promoted through supported peer-to-peer (mostly mother-to-mother) knowledge sharing. The aim of most Care Groups is to promote improved infant nutrition, improve hygiene and increase the number of children who are fully vaccinated and exclusively breastfed for the first 6 months. The behavioural changes promoted by Care Groups (such as safe infant feeding, frequent hand washing, consistent mosquito net usage, providing suitable complementary foods from 6 months old) have the potential of averting preventable deaths particularly among children under five. While a variety of approaches are used to promote improved health and nutrition for children under five, the Care Groups model was best known and frequently referenced during our discussions with key stakeholders regarding the delivery at community level of Malawi's National Multi-Sector Nutrition Policy 2018-2022. A better understanding of how Care Groups achieve their social and behaviour change results and how community-based efforts are sustained can potentially help to ensure more effective planning and budgeting for Care Group interventions and enable greater sustainability and increased coverage of infant feeding support countrywide. This realist review is designed to improve our understanding of how, why, to what extent and under what circumstances Care Groups improve infant feeding practices in low-and middle-income countries (LMICs). Methods and analysis: A realist review is a theory-driven approach to evidence synthesis. To undertake this realist review, we will gather evidence by conducting peer-reviewed and grey literature database searches in order to find peer reviewed articles, programme guidelines and evaluation reports, among other texts, associated with the implementation of Care Groups in low-and middle-income countries. Our review process has five key steps: (1) locating existing theories; (2) searching for evidence in literature; (3) selecting articles and other suitable evidence; (4) extracting data, identifying configurations of context-mechanism-outcomes; and (5) synthesising the evidence, drawing conclusions. Discussion: The results of this realist review will be written up according to RAMESES guidelines and disseminated through a stakeholder workshop in Malawi, through conference presentations and peer-reviewed publications. It is intended to improve the understanding of the potential and limits of working through Care Groups globally and among relevant Malawi Ministry of Health staff and the donor and NGO community, both internationally and within Malawi. This systematic review protocol has been submitted for registration on the PROSPERO database (receipt number: 170261).