For ethnoracially minoritized and immigrant youth, identity formation involves efforts to integrate social identities that are derived from their ethnic-racial group memberships (i.e., ethnic-racial identity) and their connection to the country in which they reside (i.e., national identity). This study investigated the extent to which these two social identities were simultaneously associated with adolescents' psychosocial adjustment via their associations with the integration of these identities (i.e., bicultural identity integration) and across adolescents' identity domains (i.e., global identity coherence). This cross-sectional study (January 2020) included a US ethnoracially diverse sample of 355 adolescents (M[subscript age] = 15.95 years; SD = 0.79; 50.4% female; 40.6% Latino/a/x, 29.0% White, 13.2% Black, 8.2% Asian, 7.0% other; 76.1% US-born; 76.9% had at least one foreign-born parent) who completed online surveys in class. Structural equation path analyses with bias-corrected bootstrapping were conducted to test a theoretical sequential mediation model of identity and adjustment. Findings indicated that national American identity explained significant variance in adolescent psychosocial adjustment (i.e., higher academic engagement and self-esteem) via its unique associations with bicultural identity integration and global identity coherence. Furthermore, sensitivity analyses revealed some support for alternate models suggesting that the examined identity constructs may work in tandem with one another to inform adolescent psychosocial adjustment. This study highlights the multifaceted nature of social identity development and provides preliminary evidence regarding how the simultaneous development of adolescents' ethnic-racial and national identities informs their psychosocial adjustment.