Transition management has emerged as a new governance approach of sustainable development. It proposes a four-level management framework, aiming to transform socio-technical systems towards sustainable development trajectories through a multi-domain and multi-actor management process. Based on this management framework, this study focuses on a particular type of actor, the systemic intermediaries, and analyzes their contributions to transition management by building an analytical framework which identifies their roles at each of the four management levels. In addition, a case study of the carbon neutrality transition in Sonderborg is conducted, the management of which has involved a systemic intermediary ProjectZero Organization. The case study has shown that the transition management has been an incremental, reflexive and dynamic process based on collaboration, learning and innovation, and the ProjectZero Organization has contributed to this process mainly by aligning actors through networking, enabling and catalyzing.