BACKGROUND: Internally displaced persons (IDPs) in Nigeria face a high burden of mental health disorders, with limited access to evidence-based, culturally relevant interventions. Life skills education (LSE) is a promising approach to promote mental health and psychosocial well-being in humanitarian settings. This study aims to evaluate the effectiveness and implementation of a culturally adapted LSE program delivered through in-person and mobile platforms among IDPs in Northern Nigeria. METHODS: This cluster-randomized hybrid type 2 effectiveness-implementation trial will be conducted in 20 IDP camps or host communities in Maiduguri, Nigeria. Sites will be randomly assigned to receive a 12-week LSE program delivered either through in-person peer support groups or WhatsApp-facilitated mobile groups. The study will recruit 500 participants aged 13 years and older. Intervention effectiveness outcomes include the primary outcome of change in post-traumatic stress disorder (PTSD) symptoms assessed using the PCL-5 scale, and secondary outcomes of depression, anxiety, well-being, and life skills acquisition. Implementation outcomes will be assessed using the Acceptability of Intervention Measure (AIM), Intervention Appropriateness Measure (IAM), and Feasibility of Intervention Measure (FIM). Both sets of outcomes will be compared between the in-person and mobile delivery groups. Quantitative data will be analyzed using mixed-effects linear regression models, while qualitative data will be examined through reflexive thematic analysis. The study will be guided by the Reach-Effectiveness-Adoption-Implementation-Maintenance (RE-AIM) framework. DISCUSSION: The RESETTLE-IDPs study addresses key gaps in the evidence base on mental health interventions for conflict-affected populations. It focuses on underserved IDP populations, evaluates the comparative effectiveness of in-person and mobile-delivered LSE, and incorporates implementation science frameworks to assess contextual factors influencing adoption, fidelity, and sustainability. The study employs a community-based participatory approach to enhance cultural relevance, acceptability, and ownership. Findings will inform the development and scale-up of evidence-based, sustainable mental health interventions for IDPs in Nigeria and other humanitarian contexts. TRIAL SPONSOR: Dalhousie University, 6299 South St, Halifax, NS B3H 4R2, Canada. TRIAL REGISTRATION: ClinicalTrials.gov, NCT06412679  Registered 15 May 2024.