School belonging is linked with socioemotional wellbeing and academic achievement, but an important question is whether school belonging or its effects vary for college or university students of minority identities. A number of outcomes associated with school belonging, including positive social relationships, perceptions of a fulfilling life, self-respect, optimism, and self-efficacy, are interlinked by the concept of socioemotional flourishing. This study aimed to assess the age-varying prevalence of and association between school belonging and flourishing among sexual or gender minority (SGM) and racial or ethnic minority (REM) students compared with non-minority students in the U.S. higher education setting. Data were drawn from a large national survey of U.S. college and university students ages 18–26, and were examined using varying-coefficient models to estimate the relation of school belonging and flourishing as a continuous function of age. SGM students (n = 6,718) had significantly lower belonging and flourishing than cisgender heterosexual students (n = 19,492) across all age points, and compared to white students (n= 16,444), REM students (n = 10,539) endorsed significantly lower belonging and flourishing at several age points. The association of belonging with flourishing was found to be significantly greater for SGM students than for cisgender heterosexual students across all ages, while age-varying associations for REM and white students were more complex. Findings of this study underline the unique importance and magnitude of the role of school belonging in socioemotional flourishing for SGM young adults, and highlight potential avenues for prevention of negative psychosocial and substance use outcomes among both SGM and REM college and university students.