Despite the adoption of the 1999 decentralization legislation, Thailand has made limited progress in devolving public service functions to local government. Primary care in particular remains largely centralized. However, upon the end of the current operational plan on decentralization, it is required that ownership and management of the subdistrict health promotion hospitals must be transferred to provincial administrative organizations. To help inform government officials and policymakers in Thailand on how to expedite the decentralization process and ensure the smooth transfer of the primary care services to local government authority, this research has three primary objectives. First, it seeks to analyze the management system and performance of subdistrict health promotion hospitals that have already been devolved to municipalities and subdistrict administrative organizations. Second, future scenarios for the transfer of primary care functions to provincial administrative organizations are formulated, using a double-variable scenario method. Third, based on findings from the first and second objectives, policy recommendations are presented. Qualitative and quantitative techniques were used to analyze data that were collected from multiple sources, including documentary review, a citizen perception survey, a survey of subdistrict health promotion hospital personnel, interviews with 27 key policymakers and subdistrict health promotion hospital directors, and focus group discussions with 58 officials from provincial administrative organizations and citizen representatives. In total, 6,304 citizens responded to the survey. Personnel from 70 subdistrict health promotion hospitals that have already been devolved to municipalities and subdistrict health promotion hospitals participated in the survey. This research finds that although small in number, the subdistrict health promotion hospitals that have successfully been transferred from the public health ministry to local administrative organizations have shown significant progress in primary care quality. Intermediate health outcomes—particularly citizens’ behavioral changes in physical activity and eating habit—in the decentralized areas continue to improve, while citizens harbor more positive attitudes towards the devolved subdistrict health promotion hospitals than those not devolved to local administrative organizations. However, there are mounting concerns among local government officials about personnel recruitment and retention, as well as continuity of the intergovernmental grants. Based on the future scenario analysis, a desirable scenario depicts a devolved primary care system in which the provincial administrative organizations have adequate management capacity, while the central government agencies proactively provide technical advice and effectively perform their regulatory function. The major policy recommendations for the relevant government agencies include: 1) accelerate the transfer of subdistrict health promotion hospitals to the provincial administrative organizations; 2) establish citizens’ consultative councils at the provincial, district, and hospital levels to facilitate citizen engagement in local health policy making; 3) develop explicit criteria for determining the amount of intergovernmental grants for the devolved primary care functions; 4) generate a list of essential primary care services and associated costs based on the Primary Care System Act of 2019 and collaborate with the National Health Security Office in reforming the health financing system by separating primary care from secondary and tertiary care; 5) strengthen citizens’ consultative councils and develop it into a central decision-making body charged with providing linkage and referrals between provincial administrative organizations and the public health ministry’s hospitals, preparing the provincial health strategy, and integrating different health databases and; 6) propose to the Ministry of Interior that it should enable the provincial administrative organizations, municipalities, and subdistrict administrative organizations to share resources, budget, and personnel in providing primary care services and financial assistance for the subdistrict health promotion hospitals