<p>The global climate change governance landscape is rapidly evolving. Non-state actors and institutions increasingly challenge the formal authority of the United Nations Framework Convention on Climate Change (UNFCCC), operating in parallel with its intergovernmental processes. In particular, multi-stakeholder partnerships (MSPs) carry out several policy functions, becoming established actors within the climate governance domain. Nevertheless, it remains unclear how MSPs’ recently established governance roles should be understood vis-à-vis the fluid global climate governance landscape. Focusing on the case of the Climate and Clean Air Coalition (CCAC), this paper shows that this MSP legitimizes its governance role through claims to epistemic authority. Illustrating how the CCAC seeks legitimacy through ‘frontstage’ practices and discourses rooted in science, I argue that epistemic authority serves as a primary tool for the CCAC to consolidate its position within the global climate governance regime. However, legitimation through epistemic authority is not necessarily sufficient to this end, as global climate non-state actors such as the CCAC face several ‘backstage’ challenges in a dense and competitive governance landscape. I conclude that the study of global climate MSPs benefits from close scrutiny of their agency and challenges, as this helps understand how these actors contribute to the evolution of global climate politics.</p>