ObjectiveWe aimed to understand how, why and in what context upskilling programmes for unregulated care providers (UCPs) to provide foot screening for systematically marginalised groups living with diabetes were implemented.DesignWe used realist synthesis based on Realist And Meta-narrative Evidence Syntheses: Evolving Standards guidance.Data sourcesWe searched the Medline, Embase, PsycINFO, CINAHL, ERIC, Web of Science Core Collection, and Scopus databases and the grey literature (Google Scholar, ProQuest Dissertations and Theses) up to November 2022.Eligibility criteriaWe included experimental and non-experimental articles in English that either described mechanisms or discussed expected outcomes for educational interventions for patients and family caregivers or healthcare providers, both regulated and unregulated. We also included articles that evaluated the impact of foot care programmes if the UCPs’ training was described.Data extraction and synthesisThe lead author extracted, annotated and coded uploaded relevant data to identify contexts, mechanisms and outcome configurations using MAXQDA (a qualitative data analysis software). We used deductive and inductive coding to structure the process. Our team members double-reviewed and appraised a random sample of 20% of articles at all stages to ensure consistency.ResultsOur search identified 52 articles. Evidence suggested the necessity of developing upskilling foot screening programmes within the context of preventive care programmes that also provide education in diabetes, and early referrals for appropriate interventions. Multidisciplinary programmes created an ideal context facilitating coordination between UCPs and their regulated counterparts. Engaging patients and community partners, using a competency-based model, and incorporating cultural competencies were determinants of success for these programmes.ConclusionThis review provides a realistic programme theory for the mechanisms used, the context in which these programmes were developed, and the expected outcomes to train UCPs to provide preventive foot care for systematically marginalised populations.PROSPERO registration numberCRD42022369208.