Humanitarian emergencies pose a significant global health challenge for children and young people’s mental and psychological health. This systematic review investigates the effectiveness of mental health and psychosocial support (MHPSS) programmes delivered to children and young people affected by humanitarian emergencies in low- and middle-income countries (LMICs). Twelve electronic databases, key websites and citation checking were undertaken. Forty-three randomised controlled trials (RCTs) published in English between January 1980 and May 2023 were included in the review. Overall, the findings suggest that cognitive behavioural therapy may improve depression symptoms in children and young people affected by humanitarian emergencies. Narrative exposure therapy may reduce feelings of guilt. However, the impact of the other MHPSS modalities across outcomes is inconsistent. In some contexts, providing psychosocial programmes involving creative activities may increase the symptoms of depression in children and young people. These findings emphasise the need for the development of MHPSS programmes that can safely and effectively address the diverse needs of children and young people living in adversarial environments.