Most traditional youth mental health interventions fail to achieve sustainable impact at scale because they overly rely on individualized, medical illness-focused models and treat youth as passive beneficiaries. citiesRISE, a multi-stakeholder initiative founded in 2017 to address these gaps, has worked with youth, communities, and professionals across five cities, as well as social innovators in over twenty countries, to develop a set of evidence-based, scalable youth mental health interventions and implementation models. The YiPEE project aims to provide robust evidence on the feasibility, adaptability, effectiveness, and cost-effectiveness of a multi-component intervention targeting the inner, social, and environmental dimensions that underpin mental health and broader NCD risk reduction outcomes, when implemented using a youth-informed and -activated approach. This will be achieved through a a mixed-methods approach, conducting a realist evaluation across the four sites (Chennai, India; Nairobi, Kenya; Cape Town, South Africa; Stockholm, Sweden) to study key implementation outcomes following the Practical Robust Implementation and Sustainability Model (PRISM) as well as the mechanisms underlying why the intervention works, for whom, and under what real-world conditions. In Chennai, YiPEE will conduct a randomized controlled trial for more robust evaluation of effectiveness and cost-effectiveness in achieving key mental health and other NCD related lifestyle behavioral outcomes. YiPEE focuses on the combination of a school-based multicomponent intervention targeting positive disruption in the inner, social, and environmental dimensions of adolescents’ mental health and a youth-informed and -activated implementation model that puts young people at the centre of transformation, working collaboratively with a range of other stakeholders.