Adolescent involvement in mental health prevention research remains limited in low-resource settings. This study examined the feasibility, acceptability, processes and perceived impacts of adolescent advisory groups (AAGs) within the ALIVE research in Colombia, Nepal and South Africa. Using a convergent mixed-methods design, we analysed data collected between October 2022 and August 2025 using surveys with adolescents (t1: n = 33; t2: n = 26), focus group discussions (n = 6 with adolescents; n = 2 with caregivers), interviews (n = 8 with adolescents; n = 5 with facilitators), process documents (n = 58) and post-session feedback (n = 7). Participation was highly valued by most adolescents, who were motivated by altruism, peer connection, skill development and project incentives. Most adolescents strongly agreed they could express their views freely (t1: 79%; t2: 81%) and felt listened to (t1:76%; t2: 81%, respectively). Participants reported experiences of trust, confidence and collective agency; challenges included stigma, unequal participation and logistical barriers. Facilitators’ relational and adaptive support appeared central to sustaining engagement. Adolescent members contributed in important ways to the ALIVE research. Adolescent involvement in prevention research in low-resource settings is feasible and can be experienced by participants as valuable.