Within the UK, peer interventions are a policy and practice priority for adults experiencing problematic substance use, alongside related co-occurring needs. The prevailing narrative emphasizes the distinctive benefit that lived experience knowledge brings to provision, yet there is limited robust evidence to verify these claims. Drawing on qualitative research with fifty participants, this article contributes vital new knowledge about the way that peer support ‘works’, presenting an empirically and theoretically informed model that outlines the mechanisms of change underlying peer worker interventions. The article introduces an original perspective by applying Békés and Hoffman’s concept of Authentic Relational Moments to explain how lived experience knowledge can be used to foster therapeutic relationships, considered a necessary foundation for change and recovery. Providing important learning for social work, it proposes a novel theory of change that defines lived experience not as intrinsically generative but as a resource that operates through a network of interrelated social mechanisms.