The transition towards the circular economy (CE) entails transformative and system-wide changes, implying involvement, alignment, and cooperation between all stakeholders at all levels. However, debate continues around how best to achieve this. Additionally, little attention has been paid to developing models for identifying and mobilising all relevant stakeholders to implement CE policies at the regional level. This study sought to remedy these issues by analysing the relevant academic literature and policy documents and making the first attempt to adjust existing models—not only for the purpose of stakeholder mapping, but also for the proposition of a living constellation of stakeholders who should be considered when designing the transition towards a CE in a regional scenario. The CE-centric quintuple-helix model developed and proposed here promotes the emergence and deployment of trilateral networks, hybrid organisations, and development/co-operation platforms. This model adopts a balanced, participatory approach that requires a new constellation of stakeholders. Its foundations are built on the traditional industry–government–academia nexus and enlarged by the inclusion of the civil society sphere and the environmental subsystem. The environment is represented as the nucleus of the model, inspiring and triggering actions by the remaining four subsystems. The model is then implemented into two European regions with CE initiatives (Spain and Greece) to demonstrate its practical application.