AbstractThis study provides insight into the current evolution of the New Development Bank (NDB). It examines the role of the agency of the global South reshaping intergovernmental organizations (IGOs) in the case of Brazil's influence on the NDB to expand its membership. In that process, this article homes in on the admission of Uruguay to the NDB as a prospective member in September 2021, the first case of NDB expansion into Latin America and the Caribbean (LAC). The study shows that the membership negotiations between Montevideo and the Bank were less rigid and formal than the procedural norms of multilateral development banks (MDBs) of the North, thanks to the collaborative agency by the various LAC actors involved. It makes the case that Uruguay's accession to the NDB will produce numerous win‐win benefits for both the country and the Bank. It also argues that the membership will inspire the future accession of other countries in the LAC region to the Bank. The study adds to the scant literature which conceptualizes the mechanics of membership expansion by small or new IGOs. The piece also adds to existing studies investigating how LAC agency has previously shaped and continues to shape MDBs.