As adolescents transition into young adulthood they experience significant behavioural, emotional, cognitive, and social change. The well-being of young adults at this stage is an important issue to address and the reason is two-fold. Firstly, there are an increasing number of reported cases of physical health problems, such as obesity and (later) cardiovascular disease as well as psychological health issues, including stress, depression and anxiety. Secondly, early ideas and patterns of behaviour relating to good physical and psychological health become crucial to the establishment of life-long habits and healthy mindsets. Of interest to the present investigation is how the transition from the support and structure of the school environment to a more independent, and potentially less structured and less monitored post-schooling environment affects young adults’ physical and psychological well-being. The present research examines how physical well-being predicts psychological well-being in a two-wave longitudinal sample (N = 213) of late adolescents transitioning from school to post-school pathways. Surveys were administered in the final year of high school (T1) and then one year later (T2). The proposed factor structure and hypothesised paths at each time point were supported by multivariate data analysis techniques, such as confirmatory factor analysis and longitudinal structural equation modelling. Results demonstrated that physical health positively predicts psychological health and perceived life quality and satisfaction (as well as sense of meaning and purpose in life at T2). These results also yielded a significant cross-time effect from T1 psychological health to T2 physical health. This research suggests other yields for adolescent health-related quality of life research including: further theoretical and conceptual clarity in the field, multidimensional and integrative research approaches and additional methodological strengths important for future research, as well as practical, educational and industry-related yields pertaining to both educational and psychological practitioners. It is concluded that the present findings hold substantive and practical significance for the well-being of young people who are transitioning from late adolescence to young adulthood.