<p dir="ltr">Late adolescence is a significant period for sociopolitical development, and empirical research suggests that being involved in politics can lead to adaptive developmental and community outcomes. As a function of democracy, all adolescents should have opportunities to engage in political activities. However, some research suggests that political activity participation is unevenly distributed across adolescent populations and can be impacted by gender/sex (Campbell & Wolbrecht, 2020; Gordon, 2008), ethnicity and race (Pritzker, 2012), and immigrant origin (Wray-Lake et al., 2018) among other sociodemographic factors. Researchers have called for increased attention to potential intersectional patterns in adolescent political engagement and the overlapping systems of power that create them (Anyiwo et al., 2018; Godfrey & Burson, 2018; Wray-Lake, 2019). This dissertation aimed to respond to that call. Guided by the Positive Youth Development framework (Lerner et al., 2005), Intersectionality Theory (Crenshaw, 1989), and Sociopolitical Development Theory (Watts et al., 2003), this dissertation study explored how belonging to intersectional sociodemographic groups based on gender/sex, ethnicity and race, and immigrant origin may be associated with political activity participation among late adolescents. Frequency of experiencing discrimination followed by four civic beliefs pertinent to adolescent sociopolitical development (moral identity, political identity, internal political efficacy, and external political efficacy) were tested as potential mechanisms. Data was drawn from the Stanford Civic Purpose Project (Damon, 2017), an ethnically and racially diverse sample of high school seniors in the U.S. (<i>N</i> = 1,551; mean<i> </i>age = 16.88 years; 46.2% Latinx, 27.9% Asian/Asian American). Structural equation modeling was used to explore identity differences in five types of adolescent political activity and test potential mechanisms via a serial mediation model.</p><p dir="ltr">Findings from this dissertation study offered support for political activity participation as a multidimensional construct. Notably, intersectional differences in civic beliefs or political activity did not emerge. However, the results still provided support for sociodemographic diversity in political activity participation, as well as diverse paths to get there. In terms of gender/sex differences, girls participated in more political activities than boys with effects of gender/sex consistently mediated by moral identity. Moreover, Latinx adolescents were involved in more activities outside of the political system including activism and creative expression compared to Asian/Asian American adolescents. Contrary to expectations, however, no differences were evidenced across immigrant origin. Lastly, results for the serial mediation model showed that discrimination experiences did not mediate the influence of sociodemographic identity on political activity participation for any subgroup of adolescents. However, direct and indirect pathways were found between frequency of experiencing discrimination and political activity via civic beliefs. Implications of these findings for future research on adolescent political activity participation are discussed.</p>