Mental health literacy interventions in school settings are growing in number and scope, yet challenges in user engagement and real-world implementation persist. The Decode Mental Health and Wellbeing Program (Decode) is a novel and innovative mental health literacy program for teachers and students that harnesses the power of social media platform-style content delivery and lived experience influencers to engage young people. Using a multi-site, multi-informant, pre-post cohort study design over a 4-week implementation period, Decode was evaluated in five Victorian government and Catholic primary and secondary schools (years 5-8) in Victoria, Australia. Data collected using surveys (teacher n = 14, student n = 159) and focus groups/interviews (teacher n = 14, student n = 41) provided insights into the program's feasibility (acceptability, implementation) and impact. Findings indicated that Decode was acceptable to both teachers (86%) and students (67%), with strong endorsement of the program's relatability, engagement, and appropriateness. The program led to improvements in student and teacher mental health literacy including knowledge of help-seeking strategies, reductions in stigma, and improved teacher-observed student mental health and wellbeing. Implementation challenges were related to timetabling of course lessons and difficulties with teachers' use of the platform hosting Decode. Ultimately, Decode shows promise as an effective intervention for bridging the gap between evidence-based mental health content and student engagement, though further work is needed to optimise its delivery and assess its long-term effects.