Low- and middle-income countries (LMICs) carry a significant proportion of the global burden of untreated mental health disorders. Peer-delivered programs offer LMICs with limited mental health professionals an opportunity to increase mental health service access. This study describes the process of adapting a lay-worker-delivered evidence-based youth mental health intervention to a peer-delivery model in Sierra Leone using participatory methods. We convened Youth Community Advisory Boards (YCABs) as partners to develop a peer-delivery model for an evidence-based intervention. In collaboration with YCABs, the Assessment, Decision, Administration, Production, Topical experts, Integration, Training, Testing (ADAPT-ITT) framework was applied to guide the adaptation. The ADAPT-ITT framework is an eight-step process to adapt evidence-based interventions. The ADAPT-ITT framework facilitated the adaptation of the Youth Readiness Intervention (YRI), an evidence-based mental health program intervention that has been delivered by adult lay-workers to the youth peer-delivery platform in Sierra Leone. The YCABs identified program modifications, including the incorporation of storytelling, refinement of metaphors, and alterations to make delivery more accessible to low-literacy youth with particular attention to gender. YCABs also provided recommendations on how to support youth facilitators in providing psychosocial support, emphasizing self-care and boundary setting to ensure high-quality intervention delivery and do-no-harm principles. Study findings suggest that the ADAPT-ITT framework can be feasibly applied to guide the intervention adaptation process in LMICs. The use of participatory methods generated modifications that reflected youth experiences, needs, and concerns as facilitators and participants. Next steps include refinement and pilot testing of the adapted intervention.