BackgroundSchool‐based mental health literacy interventions aim to prevent mental disorders and promote mental wellbeing through improving the knowledge and understanding of mental health, mental disorders, and reducing stigma. Evidence suggests that good mental health literacy helps young people recognise mental health difficulties in themselves and in others, and seek help for mental health problems. Improved help‐seeking can allow for early intervention, which prevents the progression of mental disorders and ultimately reduces the burden of mental disorders. The aim of this review is to identify and synthesise evidence on the effectiveness of school‐based mental health literacy interventions in improving help‐seeking outcomes.MethodsWe searched MEDLINE, Embase, PsycINFO, ERIC, Child Development and Adolescent Studies, British Education Index and ASSIA (June 2020). Additional searches were conducted a year later to identify any new publications (June 2021). We included randomised controlled trials (RCTs) assessing the effectiveness or cost‐effectiveness of school‐based interventions to improve help‐seeking outcomes for children and young people aged 4–18 years. Included studies were critically appraised.ResultsWe identified 11 studies investigating help‐seeking outcomes of school‐based mental health literacy interventions including a total of 7066 participants from 66 secondary schools. Overall, there is no strong evidence for the effectiveness of school‐based mental health literacy interventions in improving help‐seeking outcomes, including general attitudes towards help‐seeking, personal intentions to seek help, knowledge of when and how to seek help for mental disorders, confidence to seek help, and actual help‐seeking behaviours. None of the studies investigated the cost‐effectiveness of the interventions.ConclusionThe lack of standardised measures with established reliability and validity for help‐seeking outcomes, and the incomprehensive consideration of the multi‐faceted concepts of MH literacy and MH stigma have contributed to the scarcity of evidence for the effectiveness. Future research should focus on developing standardised measurement tools and including economic evaluations to understand pragmatic and financial aspects of school‐based mental health literacy interventions.