BACKGROUND: People living with HIV experience HIV stigma alongside a spectrum of aging-related health conditions that accelerate their vulnerability to the ill effects of loneliness and social isolation. Group-singing interventions are efficacious in improving psychosocial well-being among older people in the general population; however, the social curative effects of group singing have not been explored in relation to HIV stigma. By promoting group identification, bonding, and pride, group singing may reduce loneliness, social isolation, and other negative impacts of HIV stigma among older people living with HIV. Access to group-singing programs may be enhanced by technology. OBJECTIVE: While group singing has been extensively studied in older adults, group-singing interventions have not been adapted for older people living with HIV to target loneliness and social isolation in the context of HIV stigma. The objective of this study was to describe the systematic development of a group-singing intervention to reduce loneliness and social isolation among older people living with HIV. METHODS: In the San Francisco Bay Area between February 2019 and October 2019, we engaged older people living with HIV in a rigorous, 8-stage, community-engaged intervention adaptation process using the Assessment, Decision, Adaptation, Production, Topical Experts, Integration, Training, and Testing (ADAPT-ITT) framework. On the basis of a formative assessment of the needs and preferences of older people living with HIV, we selected an evidence-based group-singing intervention for older adults and systematically adapted the intervention components by administering them to a community advisory council (n=13). RESULTS: The result was United Voices, a 12-week hybrid (web-based and in-person) group-singing intervention for older people living with HIV. United Voices comprises 12 web-based (ie, via Zoom [Zoom Video Communications]) rehearsals, web-based and in-person drop-in helpdesk sessions, and a professionally produced final concert recording. CONCLUSIONS: Through an iterative process and in consultation with stakeholders and topic experts, we refined and manualized United Voices and finalized the design of a pilot randomized controlled trial to evaluate the feasibility and acceptability of the intervention protocol and procedures. The findings provide insights into the barriers and facilitators involved in culturally tailoring interventions for older people living with HIV, implementing intervention adaptations within web-based environments, and the promise of developing hybrid music-based interventions for older adults with HIV.