BACKGROUND:Achieving hepatitis C (HCV) elimination goals will require major policy and health service reorientation to scale up testing and treatment among people who inject drugs (PWID). To achieve this, a close partnership with peer-based drug user organisations is required. However, peer organisations have historical and ongoing difficulties in articulating the validity of their service delivery and policy advice, leading to some policy and health services resisting partnership and advice from peer-based drug user organisations. METHODS:To develop a deeper understanding of the role of peer-based drug user organisations in the HCV response, we analysed data from the W3 Project which used systems thinking methods to draw together the insights of over 90 peer staff from 10 Australian community and peer organisations in HCV and HIV. The resulting system maps were analysed to identify system dynamics and functions that need to be fulfilled for peer organisations to be influential within their community and policy system. RESULTS:We identified the interactions at a system level which can enhance or constrain the quality and influence of policy advice from peer-based drug user organisations. We found the strength of Peer-based drug user organisations to support the scale up of HCV testing and treatment was their capacity to mediate between, and navigate within, the complex community and policy/health service systems. While peer-based drug user organisations endeavour to demonstrate their capacity and credibility in terms of engagement, alignment, adaptation and influence, policy and service organisations also need recognise their own system role to value and enable peer-based drug user organisations to achieve their potential. CONCLUSION:If the HCV prevention and treatment system is to reach PWID living with HCV and achieve HCV elimination goals, then policy and health services need to invest in strengthening peer-based drug user organisations as well as recognise, value and act on quality policy advice from PWID peer leadership.