IntroductionThe Syrian crisis, followed by a financial crisis, port explosion, and COVID-19, have put enormous strain on Lebanon’s health system. Syrian refugees and the vulnerable host population have a high burden of Non-communicable Diseases (NCD) morbidity and unmet mental health, psychosocial and rehabilitation needs. The International Committee of the Red Cross (ICRC) recently introduced integrated NCD services within its package of primary care in Lebanon, which includes NCD primary health care, rehabilitation, and mental health and psychosocial support services. We aimed to identify relevant outcomes for people living with NCDs from refugee and host communities in northern Lebanon, as well as to define the processes needed to achieve them through an integrated model of care. Given the complexity of the health system in which the interventions are delivered, and the limited practical guidance on integration, we considered systems thinking to be the most appropriate methodological approach.MethodsA Theory of Change (ToC) workshop and follow-up meetings were held online by the ICRC, the London School of Hygiene and Tropical Medicine and the American University of Beirut in 2021. ToC is a participatory and iterative planning process involving key stakeholders, and seeks to understand a process of change by mapping out intermediate and long-term outcomes along hypothesised causal pathways. Participants included academics, and ICRC regional, coordination, and headquarters staff.ResultsWe identified two distinct pathways to integrated NCD primary care: a multidisciplinary service pathway and a patient and family support pathway. These were interdependent and linked via an essential social worker role and a robust information system. We also defined a list of key assumptions and interventions to achieve integration, and developed a list of monitoring indicators.DiscussionToC is a useful tool to deconstruct the complexity of integrating NCD services. We highlight that integrated care rests on multidisciplinary and patient-centred approaches, which depend on a well-trained and resourced team, strong leadership, and adequate information systems. This paper provides the first theory-driven road map of implementation pathways, to help support the integration of NCD care for crises-affected populations in Lebanon and globally.