INTRODUCTION: There is a severe shortage of specialist mental healthcare providers in low-income and middle-income countries (LMICs) affected by humanitarian crises. In these settings, talking therapies may be delivered by non-specialists, including lay workers with no tertiary education or formal certification in mental health. This systematic review will synthesise the literature on the implementation and effectiveness of talking therapies delivered by lay workers in LMICs affected by humanitarian crises, in order to develop a Theory of Change (ToC). METHODS AND ANALYSIS: Qualitative, quantitative and mixed-methods studies assessing the implementation or effectiveness of lay-delivered talking therapies for common mental disorders provided to adult survivors of humanitarian crises in LMICs will be eligible for inclusion. Studies set in high-income countries will be excluded. No restrictions will be applied to language or year of publication. Unpublished studies will be excluded. Seven electronic databases will be searched: MEDLINE, Embase, PsycINFO, PsycEXTRA, Global Health, Cochrane Library and ClinicalTrials.gov. Contents pages of three peer-reviewed journals will be hand-searched. Sources of grey literature will include resource directories of two online mental health networks (MHPSS.net and MHInnovation.net) and expert consultation. Forward and backward citation searches of included studies will be performed. Two reviewers will independently screen studies for inclusion, extract data and assess study quality. A narrative synthesis will be conducted, following established guidelines. A ToC map will be amended iteratively to take into account the review results and guide the synthesis. ETHICS AND DISSEMINATION: Findings will be presented in a manuscript for publication in a peer-reviewed journal and disseminated through a coordinated communications strategy targeting knowledge generators, enablers and users. PROSPERO REGISTRATION NUMBER: CRD42017058287.