Inadequacy in mental health care in low and middle-income countries has been an important contributor to the rising global burden of disease. The evidence base is building for innovative solutions to reduce the mental health treatment gap. However, what has largely been missing is the development of interventions which incorporate the nature of the social environment that contributes to the risk, cause, and maintenance of mental health conditions. This thesis aimed to explore the potential for social interventions to reduce the mental health treatment gap (greater than 95%) and the burden on resource-poor services in Sierra Leone. This thesis presents a methodological framework for social intervention development in low-resource settings. First, a feasibility and acceptability study examined stakeholder perceptions (n=59) using rapid ethnographic methods. Second, the evidence base and feasibility findings were modelled and validated in focus groups with Sierra Leone stakeholders (n=9) and members of the United Kingdom the Diaspora community (n=5). Third, a pilot study assessed the impact of the adapted intervention on district level mental health nurses’ knowledge, skills, attitudes, and behaviour (n=20) using qualitative data and a training evaluation tool developed co-productively with stakeholders. The intervention model endured several iterations as the context in the country changed due to the Ebola outbreak. The pilot study showed post-training improvement of skills in communicating and building relationships with service users, identifying assets and linking to community resources. Barriers to embed the model into nurse practice were identified such as stigma, reluctance to change from district health managers and policy makers, and significant financial and time constraints. This study suggests that it is important to harness local understanding of mental health conditions, build capacity of the existing workforce and enhance community engagement with services for mental health social intervention strategies to be effective.