Abstract Introduction Finland is often defined as a Nordic welfare state, characterised by universal access to healthcare and an emphasis on national and local politics in the governance of the system. In 2023, the Finnish health system was reformed by centralising organisation (purchasing and service delivery) to regional entities, as well as funding and overall governance to the state from 200 local organisations. The aims of the reform were to improve accessibility, decrease inequities, promote population health and curb growing costs. In the Finnish health system, as in other fields of society, we “find a huge number of very small changes, and a very small number of huge changes” (Cairney 2016). This makes the Finnish health system reform a rare opportunity to use a large-scale reform as a context for a study on reform implementation. Methods This research is based on document analysis and interview data collected from top regional managers. The data was analysed using a political determinants of health framework and thematic analysis. Findings The Finnish reforms were introduced by a left-centre government but implemented by a right-wing government with strong opposition to the reforms, which made full implementation challenging. The results highlight the importance of political commitment to implementation, demonstrate that reforms shape power relations at all levels of the health system and highlight how health system reforms are essentially about redistributions of power between different actors. The results also highlight the importance of contextual factors and suggest that large-scale reform should be treated as a system shock for which health systems need to prepare. Conclusions Understanding the political determinants of health and political commitment to reform is essential to implementation, as is the importance of resilience and preparedness to unexpected circumstances either due to reform-related factors or to external and contextual factors.