People forced to leave their homes, such as refugees and internally displaced persons, are exposed to various stressors during their forced displacement, putting them at risk for mental disorders. In view of the Russian military offensive in Ukraine, this review aimed at summarizing the evidence on the efficacy of transdiagnostic psychosocial interventions to promote mental health and/or to prevent mental symptoms in forcibly displaced persons of all ages. Four electronic databases and reference lists were searched for randomized controlled trials on interventions in this population from inception to March 11, 2022. Thirty-six studies were eligible, 32 were included in random-effects multilevel meta-analyses. Results on mental symptoms, M(SMD) = 0.26, p = .075, and positive mental health indicators like wellbeing, M(SMD) = 0.41, p = .182, provided no evidence for an effect favoring transdiagnostic interventions over control conditions in children/adolescents and adults. After excluding studies at risk of bias, meta-analyses on adult samples provided evidence for a small effect on mental symptoms and positive mental health, while analyses on children/adolescents yielded unchanged results. Heterogeneity was considerable, and certainty of evidence was very low. Future research should combine the imperative of humanitarian aid in face of major crises with studying forcibly displaced persons’ diverse needs to improve future interventions.