There is little practical guidance on how contextually relevant mental healthcare plans (MHCPs) can be developed in low-resource settings.

To describe how theory of change (ToC) was used to plan the development and evaluation of MHCPs as part of the PRogramme for Improving Mental health carE (PRIME).

ToC development occurred in three stages: (a) development of a cross-country ToC by 15 PRIME consortium members; (b) development of country-specific ToCs in 13 workshops with a median of 15 (interquartile range 13–22) stakeholders per workshop; and (c) review and refinement of the cross-country ToC by 18 PRIME consortium members.

One cross-country and five district ToCs were developed that outlined the steps required to improve outcomes for people with mental disorders in PRIME districts.

ToC is a valuable participatory method that can be used to develop MHCPs and plan their evaluation.

Evidence is needed for the integration of mental health into primary care advocated by the national health sector strategic investment plan in Uganda.

To describe the processes of developing a district mental healthcare plan (MHCP) in rural Uganda that facilitates integration of mental health into primary care.

Mixed methods using a situational analysis, qualitative studies, theory of change workshops and partial piloting of the plan at two levels informed the MHCP.

A MHCP was developed with packages of care to facilitate integration at the organisational, facility and community levels of the district health system, including a specified human resource mix. The partial embedding period supports its practical application. Key barriers to scaling up the plan were identified.

A real-world plan for the district was developed with involvement of stakeholders. Pilot testing demonstrated its feasibility and implications for future scaling up.