This one-year longitudinal study examined the moderating effect of perceived social support from school-based Gay-Straight Alliances in the associations between homophobic cyberbullying involvement (i.e., victimization, bystanding) and academic outcomes (e.g., classroom misconduct, school readiness, academic performance, absenteeism, school behavioural problems), measured one year later, among 470 adolescents (M[subscript age] = 16.01 years; 56% female) who identified as LGBTQIA. Perceived social support from Gay-Straight Alliances moderated the relationship between homophobic cyberbullying victimization and Time 2 classroom misconduct, absenteeism, and school behavioural problem. Furthermore, perceived social support from Gay-Straight Alliances further moderated these associations for Time 2 academic performance, school readiness, and cyberbullying victimization. Similar patterns were found for homophobic cyberbullying bystanding and Time 2 academic performance and absenteeism. Our findings highlight the need for more research on homophobic cyberbullying, the crucial role Gay-Straight Alliances can play in mitigating negative outcomes associated with homophobic cyberbullying involvement, and the development of inclusive anti-cyberbullying prevention programmes that acknowledge the needs of LGBTQIA adolescents.