Background: Despite the increasing recognition globally of the importance of mental health for sustainable development, significant barriers remain to developing mental health services in low-and middle-income countries. This study explored the particular barriers and opportunities for developing mental health services in Cambodia and how these compared with those described in other low-and middle-income countries. Methods: For this qualitative study, 18 experienced mental health professionals from different disciplines were selected using purposive sampling. Semi-structured interviews were carried out in Phnom Penh and thematic analysis of the data was completed. Results: Five key themes were identified: (1) Prioritising mental health in Cambodia, (2) Strengthening collaborations between mental health stakeholders, (3) Developing a mental healthcare model appropriate for the Cambodian culture and context, (4) Increasing the quantity and (5) Improving the quality of mental healthcare. All five themes were referred to by all 18 participants and the two most repeated themes were (2) Strengthening collaborations and (5) Improving the quality of mental healthcare. Conclusions: The themes identified in this study both corroborate previous barriers identified to developing mental health services in low-and middle-income countries and shed new light on opportunities of particular importance in Cambodia. Strengthening collaborations between key stakeholders in mental health and prioritising the quality of mental health education, training and service provision were both cited as being significant opportunities for enhancing the development of mental health services in Cambodia. These have not been widely described before as being important factors.