BACKGROUND: Intersectoral collaboration is fundamental to the provision of people-centred mental health care, yet there is a dearth of research about how this strategy operates within mental health systems in low- and middle-income countries. This is problematic given the known attitudinal, structural and resource barriers to intersectoral collaboration in high-income country mental health systems. This study was conducted to investigate intersectoral collaboration for people-centred mental health care in Timor-Leste, a South-East Asian country in the process of strengthening its mental health system. METHODS: This study employed a mixed-methods convergent design. Qualitative data elicited from in-depth interviews with 85 key stakeholders and document review were complemented with quantitative social network analysis to assess understandings of, the strength and structure of intersectoral collaboration in the Timorese mental health system. RESULTS: There was consensus among stakeholder groups that intersectoral collaboration for mental health is important in Timor-Leste. Despite resource restrictions discussed by participants, interview data and social network analysis revealed evidence of information and resource sharing among organisations working within the health and social (disability and violence support) sectors in Timor-Leste (network density = 0.55 and 0.30 for information and resource sharing, respectively). Contrary to the assumption that mental health services and system strengthening are led by the Ministry of Health, the mixed-methods data sources identified a split in stewardship for mental health between subnetworks in the health and social sectors (network degree centralisation = 0.28 and 0.47 for information and resource sharing, respectively). CONCLUSIONS: Overall, the findings suggest that there may be opportunities for intersectoral collaborations in mental health systems in LMICs which do not exist in settings with more formalised mental health systems such as HICs. Holistic understandings of health and wellbeing, and a commitment to working together in the face of resource restrictions suggest that intersectoral collaboration can be employed to achieve people-centred mental health care in Timor-Leste.