Transitions intermediaries-agents who connect diverse groups of actors involved in transitions processes and their skills, resources and expectations-are becoming more prominent in research on low-carbon transitions. Most work, however, has focused on their ability to push innovations or emerging technologies forward, emphasising their involvement in disrupting incumbent regimes or firms. However, in focusing on new entrants, often at the grassroots level, such literature runs the risk of overlooking the potentially positive role that incumbent transition intermediaries-those oriented to work with or centrally consider the interests of dominant government, market or civic stakeholders-can play in meeting sustainable energy and transport goals. In this paper, we focus specifically on five different incumbent transition intermediaries-Smart Energy GB in the United Kingdom, Energiesprong in the Netherlands, SULPU in Finland, CERTU in France, and the Norwegian Electric Vehicle Association-and explain their efforts to meet socially desirable goals of accelerating innovation or decarbonizing energy or transport systems. We ask: Why were these intermediaries created, and what problems do they respond to? How do they function? What are their longer-term strategies and aspirations? In what ways do they reflect, reinforce, or otherwise shape incumbency? In answering these questions via a comparative case study approach, the paper aims to make contributions to the study of incumbency and intermediation in the context of transitions, to identifying different types of incumbent intermediaries (market, governmental, civic), and to informing debates over energy and climate policy and politics.