Lay counselling, or the delivery of talk-based therapeutic support by people without a clinical degree, is gaining popularity as a way of addressing global shortages of mental health professionals. In Nepal, lay counselors have made significant contributions to mental health and psychosocial care over the last two decades, particularly in the aftermath of major emergencies. However, research on the longer-term integration and sustainability of lay counselling interventions remains limited. This ethnographic study explored the meaning and importance of sustainability to different stakeholders in a lay counselling program implemented following Nepal’s 2015 earthquake. We conducted participant observation in the everyday lives of five counsellors as well as four focus group discussions and 51 semi-structured interviews with counsellors and other key stakeholders. Our analysis revealed significant discrepancies in perceptions of sustainability; while organizations involved in implementing the program described it as a sustainability success due to continued government financing, counsellors emphasized their own and the government’s failure to sustain high-quality service delivery in practice. Program-level barriers included inadequate budget and remuneration, lack of clinical supervision, and poor integration within existing systems. We also identified wider sociopolitical influences on sustainability, including the social positioning of counsellors, low understanding and acceptability of counselling, and a rapidly changing political landscape. These findings reveal the need for a critical approach to sustainability in global mental health, warning against superficial engagement that prioritizes continuity of government financing over quality of care and workers’ rights. Advocating for an ecological orientation within sustainability research, we also discuss the importance of looking beyond program design factors to consider how local and national sociopolitical dynamics influence frontline service provision.