Spaces for civil society participation within intergovernmental negotiations on sustainability have multiplied since the 1992 Earth Summit. Such participatory spaces are often uncritically accepted as a remedy for an assumed democratic deficit of intergovernmental policymaking. I argue, however, that civil society’s capacity to democratize global sustainability governance is constrained by the limited influence of these spaces on policymaking. The article explores the relationship between the format of participatory spaces and their influence on the negotiations of the Sustainable Development Goals. It finds that civil society is more likely to influence within informal and exclusive participatory spaces, and when these spaces are provided early in the negotiating process, at international and national level. This reveals a democracy–influence paradox, as the actors with the capacities to engage repeatedly and informally with negotiators are seldom those that are most representative of global civil society.