Populations affected by humanitarian crises, including conflict, disasters and displacement, are frequently exposed to elevated psychological distress, while access to mental health services remains scarce. Problem Management Plus (PM+), a low-intensity psychological intervention developed by the World Health Organization, has shown clinical efficacy. However, evidence on its implementation in humanitarian contexts remains limited. This systematic review aimed to synthesize available evidence on the implementation outcomes of PM+ and its delivery formats (individual, group and digital) in such settings. The review included individual PM+, group PM+ and Step-by-Step.

Following PRISMA 2020 guidelines, we systematically searched four databases (PubMed, Scopus, Web of Science and CENTRAL) for studies published up to June 2025. Eligible studies included populations in humanitarian settings receiving PM+ in any format and reported at least one implementation outcome based on Proctor’s framework (acceptability, adoption, appropriateness, feasibility, fidelity, cost, penetration and sustainability). Data extraction and quality appraisal were conducted independently by two reviewers. The protocol for this systematic review was prospectively registered in PROSPERO (Registration No. CRD42024551943).

Of 2093 records screened, 23 studies met inclusion criteria, representing 5377 participants across diverse humanitarian contexts. Feasibility (70% of studies) and acceptability (65%) were the most frequently assessed outcomes, with consistently positive findings, including adequate recruitment, retention and cultural adaptability of PM+. Evidence was strongest for participant and provider acceptability and feasibility of delivery, whereas system-level outcomes such as sustainability, adoption, penetration and cost were rarely reported. Delivery by trained non-specialist providers was common and supported by supervision structures. Fidelity assessments (43%) demonstrated high adherence to intervention manuals. In contrast, sustainability (9%) and cost evaluations (17%) were infrequently reported. Barriers to implementation included stigma, population mobility and resource constraints, while facilitators included contextual adaptation, community engagement and ongoing supervision.

PM+ demonstrates strong feasibility and acceptability when delivered by trained non-specialist providers in humanitarian contexts. However, gaps remain in evidence on long-term sustainability, cost-effectiveness and policy integration. The limited availability of system-level implementation data constrains conclusions regarding large-scale integration of PM+ in humanitarian settings. Future research should employ standardized implementation science metrics and focus on strategies to enhance scalability and embed PM+ within existing health systems.