This is the first report of the large-scale utilization of migrants as health volunteers in a migrant primary-healthcare program. The program recruited migrants who volunteered to serve their communities. This study explores the identities of these volunteers, their relationship with program management, and their attitudes. The study also investigates the impact of the volunteers, from the migrants’ and healthcare workers’ perspective. The study was conducted in two provinces, Tak (northern Thailand) and Samut Sakhon (central Thailand). Primary and secondary information was collected. Mixed methods, comprising in-depth interviews, observation and questionnaires, were used to gather primary data from three groups of participants—migrant volunteers, migrants and healthcare workers. Secondary data, and in-depth interviews with healthcare workers, showed that migrant volunteers made a significant contribution to the provision of both preventive and curative services. The quantitative study covered 260 migrant volunteers and 446 migrants. The results found that <5% of volunteers were selected by the community. Almost all attended a training course. Most were assigned to be health communicators; four stated they did nothing. Volunteers’ attitudes were very positive. Most migrants reported that the volunteers’ work was useful. It was concluded that the migrant health-volunteer program did help deal with migrant health problems. However, management of the program should be closely considered for more effective outcomes.