Sub-Saharan African adolescents living with HIV face challenges to antiretroviral therapy (ART) adherence. Poor mental health drives nonadherence but can be improved with cognitive behavioral therapy (CBT). CBT delivered by peers may strengthen effects while building capacity for sustainment in low-income countries. This case study retrospectively applied the Exploration Preparation Implementation Sustainment framework to characterize the execution of the Kigali Imbereheza Project, a 2-arm individually randomized group controlled trial of Trauma-Informed Adherence-Enhanced CBT (TI-CBTe) delivered by Rwandan youth leaders (YLs) to adolescents living with HIV. YL (n = 14, 43% female, M = 22.71 years) had confirmed HIV and self-reported ART adherence >95%. Participants (n = 356, 51% female, M = 16.78 years) living with HIV were randomized to TI-CBTe or usual care. Two YLs co-led TI-CBTe sessions over 2 months for a total of 12 hours, while other YL observed and rated fidelity. Participants reported on YL competence. Additional data evaluated feasibility, acceptability, uptake, and fidelity. In the Exploration phase, focus groups, stakeholder meetings, and individual interviews revealed strong consensus for delivering TI-CBT to reduce adolescent depression and trauma and improve ART adherence. In the Preparation phase, curriculum revisions were made, YLs were successfully trained, and a cascading supervision model was established. In the Implementation phase, YL delivered TI-CBTe with close monitoring and supervision. Findings revealed strong feasibility, acceptability, uptake, and fidelity, increasing the likelihood of Sustainment. Exploration Preparation Implementation Sustainment can guide implementation planning and delivery and evaluate implementation outcomes.