Peer education is widely used as a health promotion strategy. However, few efforts have been undertaken to understand the implementation of peer-led health promotion programs (HPPs). This multiple-case study identifies factors facilitating the implementation of a peer-led HPP for older adults presenting with fear of falling ("Vivre en quilibre") and their mechanisms of action. It used a conceptual framework postulating factors that may influence peer-led HPPs implementation and mechanisms through which such factors may generate implementation outcomes. Six independent-living residences for older adults in Quebec (Canada) implemented "Vivre en quilibre" as part of a quasi-experimental study. Implementation factors and outcomes were documented through observation diaries, attendance sheets, peers' logbooks, questionnaires administered to participants and semi-structured interviews conducted among peers, activity coordinators of residences and a subgroup of participants. The analysis revealed three categories of factors facilitating program implementation, related to individuals, to the program and to the organizational context. Three action mechanisms identified in the framework (interaction, self-organization and adaptation) were facilitated by some of these factors. These findings support the application of the peer-led program implementation conceptual framework used in this study and provide insights for practitioners and researchers interested in implementing peer-led HPPs.