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).