The roles of public actors in promoting the industrial circular economy is uncharted, despite sustainable actions often resulting from collaboration between these actors and private actors. This study therefore illuminated (1) what roles public actors take on in the operation of an eco-industrial park (EIP) and (2) how these roles occur within the actor structure of an EIP? Correspondingly, the research conducted two qualitative case studies on EIPs where public entities are essential actors and analyzed these public spaces via the qualitative content analysis of primary and secondary data. Study 1 extensively analyzed 20 EIP cases around the world. The analysis uncovered six roles played by public actors in EIPs: operator, organizer, financer, supporter, policymaker, and regulator. Study 2 involved a longitudinal exploration of four national EIP cases, an examination of identified roles, and an ecosystem visualization mapping of what positions public actors can assume in an EIP. The research contributes to the literature primarily through the identification of roles, which show how public actor involvement in EIPs can be multifaceted and crucial in successfully operating an EIP. The research also offers new insights and a model of public actor roles in EIPs, serving as a tool for these actors to self-reflect and understand the functions that they can serve in aiming for sustainable EIP operations.