While nation-states remain primary protagonists in global governance processes, it is increasingly recognized that non-state actors (NSAs) are key players in areas ranging from human rights and civil conflict to infectious disease and nuclear non-proliferation. The area of climate change is an illustrative example. NSAs have been active participants in the margins of the Conference of Parties (COP), the annual meeting of Parties to the UN Framework Convention on Climate Change (UNFCCC), since its inception in 1995 by holding side-events and protests, raising awareness, lobbying, etc. NSAs have also contributed to the development of a “regime complex” in climate governance at the same time. Yet, the determinants and effects of that participation are not well understood. The COP offers a unique opportunity to examine one piece of this puzzle; namely, the factors that enable and motivate NSAs to participate in the design and implementation of international agreements. We use an original dataset of NSA participants at the COP from 1995 to 2016, to examine whether NSAs are well positioned to help states overcome key barriers to cooperation. As NSAs ramp up their participation in climate governance and elsewhere, this study offers insight into their motivations and potential impact on governance outcomes.