Purpose: An emerging literature documents that sexual minority youth experience significantly and substantially worse health than their heterosexual peers, but few studies have examined the intervening mechanisms linking adolescents' sexual orientation to their health outcomes. This study hypothesized that social support from parents and friends and school belonging would act as important mediators of this relationship and is among the first to test this proposition empirically. Methods: The analyses used rich data from an Australian national probability sample of 14-15-year olds (Longitudinal Study of Australian Children, n = 3204) and regression models to estimate the associations between sexual attraction and four high-quality indicators of adolescent health/well-being capturing health-related quality of life, socio-emotional functioning, depressive symptoms, and life satisfaction. Mediation tests were subsequently performed to quantify the extent to which three scales capturing social support from parents and friends and school belonging mediated the relationships identified. Results: Sexual minority status, social support from parents and friends, and school belonging were significantly related to all health/well-being outcomes. Sexual minority adolescents reported significantly lower levels of support and belonging. Collectively, the support and belonging variables were responsible for 49%-70% of the associations between sexual minority status and the health/well-being outcomes, with school belonging being the most important mediator. Conclusion: These findings have important implications for health equity policy and practice. They suggest that interventions designed to improve the health/well-being of sexual minority adolescents should be directed at eliciting enhanced social support from families and peers and fostering integration at school. School-based interventions may be particularly fruitful.