This article examines how the Group of Twenty (G20) became a hub of decentralizing authority in global economic governance since the 2008–09 global financial crisis. It analyzes how this forum responded to the crisis by decentralizing authority away from the Group of Seven/Eight (G7/8) and integrating more diverse actors and networks in global governance. The G20 also became an important hub for diffusing new policy norms and practices. These global crisis effects are linked to international authority shifts since the Cold War. The analytical approach combines, especially, social constructivist tools from the field of International Relations and insights from the sociology of professions literature. This involves analysis of strategic, political, and cognitive dimensions of authority, and a focus on the influence of global governance networks in G20 policy processes and practices. The research includes participant observation, semi-structured interviews and personal discussions with members of such G20 governance networks. The article indicates how the G20’s role as a driver and conduit for shifts in global authority was augmented by the global financial crisis.