Global public-private partnerships for sustainable development have been framed as new instruments that can increase the democratic credentials and effectiveness of global governance. This article revisits 10 years of scholarship and practice of the 348 Johannesburg partnerships, adopted at the 2002 World Summit on Sustainable Development and reaffirmed at the UN Rio+20 summit in 2012. The article analyzes the contending processes of legitimation and delegitimation of partnerships. First, it makes a quantitative assessment of the Johannesburg partnerships to examine to what extent they correspond to the UN's discursive legitimation of partnerships as implementation tools and deliberative mechanisms. Second, drawing upon interviews with civil society and UN officials, we argue that the Rio+20 summit marked the delegitimation of Johannesburg partnerships, aligned with the phase-out of the Commission on Sustainable Development. Yet, the idea of partnerships as such was relegitimized as a symbolic asset. Partnering is a legitimation strategy for UN agencies to maintain their relevance and mission in an era when multilateralism relies on collaboration between state, market, and civil society actors.