Thailand achieved full population coverage of financial protection for health care in 2002 with successful implementation of the Universal Coverage Scheme (UCS). The three public health insurance schemes covered 98.5% of the population by 2015. Current evidence shows a high level of service coverage and financial risk protection and low level of unmet healthcare need, but the path toward UHC was not straightforward. Applying the Political Economy of UHC Reform Framework and the concept of path dependency, this study reviews how these factors influenced the evolution of the UHC reform in Thailand. We highlight how path dependency both set the groundwork for future insurance expansion and contributed to the persistence of a fragmented insurance pool even as the reform team was able to overcome certain path inefficient institutions and adopt more evidence-based payment schemes in the UCS. We then highlight two critical political economy challenges that can hamper reform, if not managed well, regarding the budgeting processes, which minimized the discretionary power previously exerted by Bureau of Budget, and the purchaser-provider split that created long-term tensions between the Ministry of Public Health and the National Health Security Office. Though resisted, these two changes were key to generating adequate resources to, and good governance of, the UCS. We conclude that although path dependence played a significant role in exerting pressure to resist change, the reform team's capacity to generate and effectively utilize evidence to guide policy decision-making process enabled the reform to be placed on a "good path" that overcame opposition.