Research on the psychosocial care (PSC) of unaccompanied minor refugees (UMRs) has mainly taken a socioepidemiological approach and has focused on the perspectives of experts in the field. In contrast, the knowledge concerning the differing context factors and the underlying mechanisms of current PSC which could inform policy recommendations is scant. The study aims at unravelling the contexts, mechanisms and outcomes of PSC for UMRs. For a realist review (RR), scientific evidence and gray literature were synthesised consistent with the RAMESES publication standards for realist synthesis. Based on an iterative keyword search in electronic databases (e.g., PubMed) and screening, 34 works from 2005 to 2019 were included in a realist synthesis. Theory-informed context–mechanism–outcome configurations (CMOs) were extracted, to explain underlying processes and mechanisms. Characterised by their interrelatedness, the dominant CMOs included the UMRs’ intersections of transitions (e.g., adolescence and migration), their needs for culture-, and gender-sensitive PSC, and the undersupply of PSC. These contexts and outcomes are mediated by pre-, peri- and post-migratory stressors as well as care structures and are moreover influenced by overarching discourses and concepts. They comprise adverse and beneficial mechanisms in the PSC of UMRs. The existing literature grasps the PSC of UMRs by different disciplines and approaches but does not offer a comprehensive overview on micro–macro intersections and included discourses. The inclusion of lay perspectives and an intersectional approach could inform health service research. The reflection of UMR-related categorical constructs of resilience and vulnerability, discourses of othering, as well as restrictive health policies may guide policy recommendations.