Abstract Introduction Health systems around the world are moving towards Universal Health Coverage, which is included in the Sustainable Development Goals. However, the journey towards UHC began decades ago, with countries in Europe introducing national health services following World War II. This was mirrored in Canada and, more recently, countries in Latin America introduced health reforms as part of broader social movements. Since the millennium, reforms have also taken place in Low and Middle Income Countries as well as High Incomes Countries. However, because the introduction of UHC often necessitates far-reaching reforms, countries face significant challenges along the path of policy implementation. Methods A realist review explored international experiences of introducing and implementing UHC. Embase, Medline and Web of Science were searched. Descriptive, inductive and deductive realist analysis aided the development of Context, Mechanism, Outcome Configurations, alongside stakeholder engagement. Findings How countries go about establishing UHC depends on their social, political, cultural and economic contexts. For reforms to be facilitated, there must be cohesion and commitment across all systems, as well as the functions of financing, governance and service delivery. This includes political support, often underpinned by legislation framing healthcare as a human right, as well as communication between stakeholders and the development of a strong primary care sector. Conversely, fragmentation across these systems and functions pose significant barriers to reform. Conclusions Examining international experiences of UHC reforms supports learning around the factors that facilitate or challenge implementation. These learnings empower policy makers and health system leaders by providing roadmaps for reform implementation. Finally, this research provides insights into health inequities that are rebalanced through the implementation of UHC reforms.