Abstract Background In addition to healthcare entitlements, ‘migrant-friendly health services’ in Thailand include interpretation and cultural mediation services which aim to reduce language and cultural barriers between health personnel and migrants. Although the Thai Government started implementing these services in 2003, challenges in providing them still remain. This study aims to analyse the health system functions which support the interpretation and cultural mediation services of migrant health worker (MHW) and migrant health volunteer (MHV) programmes in Thailand. Methods In-depth interviews were conducted in two migrant-populated provinces using purposive and snowball sampling. A total of fifty key informants were recruited, including MHWs, MHVs, health professionals, non-governmental organisation (NGO) staff and policy stakeholders. Data were triangulated using information from policy documents. The deductive thematic analysis was classified into three main themes of evolving structure of MHW and MHV programmes, roles and responsibilities of MHWs and MHVs, and supporting systems. Results The introduction of the MHW and MHV programmes was one of the most prominent steps taken to improve the migrant-friendliness of Thai health services. MHWs mainly served as interpreters in public facilities, while MHVs served as cultural mediators in migrant communities. Operational challenges in providing services included insufficient budgets for employment and training, diverse training curricula, and lack of legal provisions to sustain the MHW and MHV programmes. Conclusion Interpretation and cultural mediation services are hugely beneficial in addressing the health needs of migrants. To ensure the sustainability of current service provision, clear policy regulation and standardised training courses should be in place, alongside adequate and sustainable financial support from central government, NGOs, employers and migrant workers themselves. Moreover, regular monitoring and evaluation of the quality of services are recommended. Finally, a lead agency should be mandated to collaborate with stakeholders in planning the overall structure and resource allocation for the programmes.