Abstract Background A large proportion of Syrians have been exposed to potentially traumatic events, multiple losses, and breakdown of supportive social networks and many of them have sought refuge in host countries where they also face post-migration living difficulties such as discrimination or integration problems or both. These adversities may put Syrian refugees at high risk for common mental disorders. In response to this, the World Health Organization (WHO) developed a trans-diagnostic scalable psychological intervention called Problem Management Plus (PM+) to reduce psychological distress among populations exposed to adversities. PM+ has been adapted for Syrian refugees and can be delivered by non-specialist peer lay persons in the community. Methods A randomized controlled trial (RCT) will be conducted with 380 Syrian refugees in Turkey. After providing informed consent, participants with high levels of psychological distress (scoring above 15 on the Kessler-10 Psychological Distress Scale (K10)) and functional impairment (scoring above 16 on the WHO Disability Assessment Schedule 2.0, or WHODAS 2.0) will be randomly assigned to Group PM+/enhanced care as usual (Group PM+/E-CAU) (n = 190) or E-CAU (n = 190). Outcome assessments will take place 1 week after the fifth session (post-assessment), 3 months after the fifth session and 12 months after baseline assessment. The primary outcome is psychological distress as measured by the Hopkins Symptom Checklist (HSCL-25). Secondary outcomes include functional impairment, post-traumatic stress symptoms, self-identified problems, and health system and productivity costs. A process evaluation will be conducted to explore the feasibility, challenges and success of the intervention with 25 participants, including participants, facilitators, policy makers and mental health professionals. Discussion The treatment manual of the Syrian-Arabic Group PM+ and training materials will be made available through the WHO once the effectiveness and cost-effectiveness of Group PM+ have been established. Trial registration Clinical Trial Registration: ClinicalTrials.gov Identifier NCT03960892. Unique protocol ID: 10/2017. Prospectively registered on 21 May 2019.