The outbreak of Coronavirus Disease 2019 (COVID-19) has threatened health and well-being in all populations. This impact is also deepening structural inequalities for migrant workers in Thailand. Due to their vulnerability and limited opportunity to access health services, they have greater risks in many health aspects compared to other populations. This qualitative study sought to examine the key health concerns and barriers during the COVID-19 pandemic on healthcare access among migrant workers in Thailand through the lens of policymakers, healthcare professionals, experts on migrant health, and migrant workers. We conducted 17 semi-structured in-depth interviews of stakeholders from health and non-health sectors in Thailand from July to October 2021. The interviews were transcribed and analyzed using both deductive and inductive thematic approaches. Thematic coding was applied. The results showed that financial constraints were a major barrier for healthcare access among migrant workers. These included affordability of healthcare and difficulty accessing funds (migrant health insurance). Structural barriers included some health facilities opening for emergency cases only. Insufficient healthcare resources were profound during the peak of positive cases. Cognitive barriers included negative attitudes and diverse understanding of healthcare rights. Language and communication barriers, and a lack of information also played an important role. Conclusion, our study highlights healthcare access barriers to migrant workers in Thailand during the COVID-19 pandemic. Recommendations for future resolution of these barriers were also proposed.