It is well established that physical activity has positive associations with mental wellbeing, and can protect against ill-being and mental health disorders. Further evidence suggests that in general, the most active young people continue to be the most active during adulthood. This infers that more active young people might be at less risk of poor mental health across future life stages. Findings from our recent systematic review (in press) suggested that there was reasonably consistent evidence for a beneficial effect of activities performed between the ages of 5-17 for depression at least 12 months later. Findings relating to anxiety and wellbeing were equivocal and require further research. The current study aims to take an evidence-based approach using the conclusions of our systematic review to direct research methodology. Findings will have implications for public health policy by expanding our understanding of active living in youth and the potiential impact this has on self-reported mental health across future life stages.