Findings from longitudinal research, globally, repeatedly emphasise the importance of taking an early life course approach to mental health promotion; one that invests in the formative years of development, from early childhood to young adulthood, just prior to the transition to parenthood for most. While population monitoring systems have been developed for this period, they are typically designed for use within discrete stages (i.e., childhood or adolescent or young adulthood). No system has yet captured development across all ages and stages (i.e., from infancy through to young adulthood). Here we describe the development, and pilot implementation, of a new Australian Comprehensive Monitoring System (CMS) designed to address this gap by measuring social and emotional development (strengths and difficulties) across eight census surveys, separated by three yearly intervals (infancy, 3-, 6-, 9- 12-, 15-, 18 and 21 years). The system also measures the family, school, peer, digital and community social climates in which children and young people live and grow. Data collection is community-led and built into existing, government funded, universal services (Maternal Child Health, Schools and Local Learning and Employment Networks) to maximise response rates and ensure sustainability. The first system test will be completed and evaluated in rural Victoria, Australia, in 2022. CMS will then be adapted for larger, more socio-economically diverse regional and metropolitan communities, including Australian First Nations communities. The aim of CMS is to guide community-led investments in mental health promotion from early childhood to young adulthood, setting secure foundations for the next generation.