Depression and anxiety pose a significant burden during adolescence, which may have consequences for adulthood and future generations. The mental health needs of children and adolescents in low- and middle-income countries are not adequately addressed due to a lack of availability and access to services, and limited intervention research in these contexts. Universal school-based interventions provide a unique and potentially scalable opportunity to prevent and address mental health concerns amongst children and adolescents in low- and middle-income countries. This systematic review aimed to identify and provide a narrative synthesis of universal school-based programmes delivered to children (aged 6-18 years) in low- and middle-income countries reporting on anxiety and/or depression outcomes. We searched Academic Search Premier, ERIC, PsycINFO, PubMed, Scopus, Web of Science, and ProQuest Dissertations using a pre-specified search strategy. Of the 12,478 articles identified, 12 studies met our inclusion criteria and were included in this review. The studies included report on a variety of interventions differing in approach, format and content. Given the small number of studies and concerns with study quality, we are unable to conclude that universal school-based interventions may reduce symptoms of anxiety and depression in children in low- and middle-income countries.