The transition from adolescence to emerging adulthood is a critical period of development which may have a profound and long-lasting impact on an individual’s health. The physical, affective, and cognitive changes which occur in emerging adulthood leave young people susceptible to experiencing negative mental health outcomes. Engaging in healthy behaviours such as being physically active, limiting screen time, not binge drinking, and avoiding tobacco and marijuana may help support positive mental health outcomes among emerging adults; however, there has been limited research on the synergistic role by multiple lifestyle behaviors on mental health during this developmental period. Utilizing data from the ADAPT cohort study (n = 493, 68.3% female, 15-18 years at baseline), this study analyzed the prospective relationship between self-reported levels of moderate-to-vigorous intensity physical activity, recreational screen time, sleep, binge drinking, tobacco smoking and marijuana use in adolescence and emerging adulthood with psychological distress and mental wellbeing assessed during emerging adulthood using latent profile and latent transition analysis. Three profiles were observed during adolescence, including the majority being classified as moderately active abstainers, 17% being classified as high screen users and 9% being classified as active partiers. During emerging adulthood, participants were relatively evenly split across the four profiles which included highly active moderate partiers (23%) moderately active moderate partiers (24%), inactive abstainers (31%), and inactive partiers (22%). Adolescents classified into the profile characterized by the healthiest patterns of lifestyle behaviors at baseline reported fewer symptoms of psychological distress during emerging adulthood compared to adolescents who were partiers, and better mental wellbeing than adolescents who were high screen users. Latent transition analysis showed that participants generally transitioned to a range of less healthy profiles during emerging adulthood. There was no significant difference in indicators of mental health among participants who transitioned from the healthiest profile in adolescents to various less healthy profiles as emerging adults. Collectively, these results highlight the need to support adolescents to engage in a range of healthy lifestyle behaviors to reduce psychological distress and promote mental wellbeing during their transition to emerging adulthood.