BACKGROUND: Mental health issues and disorders are major public health challenges, particularly in low- and middle-income countries in Southeast Asia, where chronic shortages in mental health services and human resources exist. The development of effective and accessible mental health systems in Southeast Asia will require evidence based psychological and social interventions. This systematic review provides a narrative synthesis of the evidence on the effectiveness of such interventions for mental health issues and disorders in Southeast Asia. METHODS: A comprehensive literature search of 7 electronic databases (PsycINFO, Medline (Ovid), Cochrane library, EMBASE, SCOPUS, APA PsycArticles, and Social Care Online) was undertaken. RESULTS: Thirty two studies employing RCT designs to evaluate the effectiveness of a range of psychological and social mental health interventions on a number of different mental health outcomes were included in this review. The disparate intervention programmes reviewed were categorised as: lay delivered, yoga, aerobic and/or meditation based, cognitive behavioural therapy oriented, eye movement desensitization and reprocessing based (EMDR), health worker delivered, and hybrid programmes. The majority of the studies included in this review were of low to moderate quality due to the variability in the quality of the study design. The highest quality, and most promising evidence came from the evaluations of lay delivered interventions. This evidence demonstrates the feasibility and potential sustainability of implementing such interventions in resource constrained contexts. CONCLUSIONS: The review findings indicate that a disparate array of mental health interventions can be implemented effectively in a range of Southeast Asian mental health and health settings. There is a clear need for significantly more research however, through higher quality and larger scale RCTs before it will be known more definitively, if these interventions are effective, and for whom they are most effective in different Southeast Asian contexts.