PurposeGiven the complex nature of integrated care systems (ICSs), the geographical spread and the large number of organisations involved in partnership delivery, the importance of leadership cannot be overstated. This paper aims to present novel findings from a rapid realist review of ICS leadership in England. The overall review question was: how does leadership in ICSs work, for whom and in what circumstances?Design/methodology/approachDevelopment of initial programme theories and associated context–mechanism–outcome configurations (CMOCs) were supported by the theory-gleaning activities of a review of ICS strategies and guidance documents, a scoping review of the literature and interviews with key informants. A refined programme theory was then developed by testing these CMOCs against empirical data published in academic literature. Following screening and testing, six CMOCs were extracted from 18 documents. The study design, conduct and reporting were informed by the Realist And Metanarrative Evidence Syntheses: Evolving Standards (RAMESES) training materials (Wong et al., 2013).FindingsThe review informed four programme theories explaining that leadership in ICSs works when ICS leaders hold themselves and others to account for improving population health, a sense of purpose is fostered through a clear vision, partners across the system are engaged in problem ownership and relationships are built at all levels of the system.Research limitations/implicationsDespite being a rigorous and comprehensive investigation, stakeholder input was limited to one ICS, potentially restricting insights from varied geographical contexts. In addition, the recent establishment of ICSs meant limited literature availability, with few empirical studies conducted. Although this emphasises the importance and originality of the research, this scarcity posed challenges in extracting and applying certain programme theory elements, particularly context.Originality/valueThis review will be of relevance to academics and health-care leaders within ICSs in England, offering critical insights into ICS leadership, integrating diverse evidence to develop new evidence-based recommendations, filling a gap in the current literature and informing leadership practice and health-care systems.