BackgroundThe burden of common mental disorders in low and middle-income countries (LMICs) is growing with little known about how to allocate limited resources to reach the greatest number of people undergoing instances of significant psychological distress. We present a study protocol for a multicentre, parallel-group, superiority, randomised controlled trial.Methods and analysisAdults with significant psychological distress (K10 score ≥20) will be randomised to receive a stepped care programme involving a self-guided course (Doing What Matters) followed by a more intensive group programme (Problem Management Plus) or the self-guided course alone, both of which will take place in addition to enhanced treatment as usual comprising of a follow-up referral session to available services within the community. We will include 800 participants. An intent-to-treat and completer analysis will explore the impact of the stepped model of care on anxiety and depression symptoms (as measured by the Hopkins Symptom Checklist; HSCL-25) at 24 weeks from baseline. Secondary outcomes include positive psychological well-being, agency, changes in patient-identified problems, quality of life and cost-effectiveness. Linear mixed models will be used to assess the differential impact of the conditions over time. Analyses will focus on the primary outcome (HSCL-25) and secondary outcomes (agency subscale, WHO Well-Being Index, WHO Disability Assessment Schedule V.2.0, EQ-5D, Psychological Outcomes Profiles Scale) for both conditions, with the main outcome time point being the 3-month follow-up, relative to baseline.Ethics and disseminationThis will be the first randomised controlled trial to assess the benefits of a stepped model of care to addressing psychological distress in a LMIC setting. Results will provide important insights for managing limited resources to mental healthcare in these settings and will be accordingly disseminated to service providers and organisations via professional training and meetings, and via publication in relevant journals and conference presentations. We will also present these findings to the Jordanian Ministry of Health, where this institute will guide us on the most appropriate format for communication of findings, including written reports, verbal presentations and/or brochures. Ethical approval was obtained from the University of Jordan School of Nursing Research Ethics Committee (number: PF.22.10).Trial registration numberACTRN12621000189820p; Australian New Zealand Clinical Trials Registry.