We used qualitative, quantitative, and observational methods to assess the feasibility, acceptability, and potential efficacy of Proyecto Orgullo (PO), a pilot community mobilisation intervention to decrease sexual risk, promote health-seeking behaviours, and facilitate personal and community empowerment among gay men (GM) and transgender women (TW) in Peru. PO was adapted from Mpowerment and Hermanos de Luna y Sol, two US interventions. PO included six interrelated core elements: (1) Self-reflection Small Group sessions; (2) Supporting peers in HIV prevention; (3) Mobilisation Activities addressing HIV, GM/TW issues, and community empowerment; (4) A Core Group (staff + GM/TW volunteers) designing/implementing those activities; (5) A Project Space; (6) Publicity. PO included specific components for TW, but promoted that GM/TW, who historically have not worked well together, collaborate for a common goal. We found that PO was embraced by GM/TW. PO positively influenced GM/TW’s HIV prevention beliefs, self-efficacy, and behaviours; provided social support and created community; facilitated individual and community empowerment; achieved that GM/TW collaborate; and established a functional Community Centre for socialising/conducting mobilisation activities. Community mobilisation strategies, lacking from HIV prevention efforts in Peru but considered key to HIV prevention, can help improve health-seeking behaviours and consolidate social norms supporting preventive behaviours among GM/TW.