Abstract Background A considerable evidence base has been produced in recent years highlighting the effectiveness of brief scalable psychological interventions for people living in communities exposed to adversity. However, practical guidance on how to scale up these interventions to wider populations does not exist. In this paper we report on the use of Theory of Change (ToC) to plan the scale up of the World Health Organization’s flagship low intensity psychological intervention “Problem Management Plus” (PM+) for Syrian refugees in Turkey. Methods We conducted a one-day ToC workshop in Istanbul. ToC is a participatory planning process used in the development, implementation and evaluation of projects. It is similar to driver diagrams or logic models in that it offers a tool to visually present the components needed to reach a desired long-term outcome or impact. The overall aim of ToC is to understand the change process of a complex intervention and to map out causal pathways through which an intervention or strategy has an effect. Results Twenty-four stakeholders (including governmental officials, mental health providers, officials from international/national non-governmental organisations, conflict and health researchers) participated in the ToC workshop. A ToC map was produced identifying three key elements of scaling up (the resource team; the innovation and the health system; and the user organisation) which are represented in three distinct causal pathways. Context-specific barriers related to the health system and the political environment were identified, and possible strategies for overcoming these challenges were suggested. Conclusion ToC is a valuable methodology to develop an integrated framework for scaling up. The results highlight that the scaling up of PM+ for Syrian refugees in Turkey needs careful planning and investment from different stakeholders at the national level. Our paper provides a theoretical foundation of the scaling up of PM+, and exemplifies for the first time the use of ToC in planning the scaling up of an evidence-based psychological intervention in global mental health.