How does leadership affect the performance of informal institutions? Leadership in BRICS is particularly puzzling: this informal institution rapidly grows despite the disparate interests of its members, some of which are in longstanding conflict. This article examines how three forms of leadership–intellectual, entrepreneurial, and structural–affect institutional performance using BRICS cooperation data. It demonstrates the importance of intellectual leadership, particularly in strategically framing the cooperation problem in a way that creates mutual gains, as essential for realising collective outcomes in informal institutions. Collective action is catalyzed through the interplay of the three leadership forms. However, the activating function of intellectual leadership–paired with follow-up activities if it initially fails–shapes the performance of these institutions. This study proposes new directions for exploring the leadership-performance nexus in informal institutions and within BRICS, a key player seeking to reform global economic governance.