Under the Cardoso presidency (1995–2002), Brazil adopted a reactive and defensive posture on trade liberalization. However, when Lula da Silva came into power in 2003, Brazil took a more offensive and proactive position on the issue in creating the G-20 and putting forward proposals of its own. How can this shift in the Brazilian negotiating position be explained? The main argument is that under the Lula da Silva administration, Brazil’s position in the Doha round primarily reflected domestic political constraints on multilateral trade cooperation. Three domestic dynamics shaped the national preference for Brazil: a heterogeneous governing coalition with a high number of veto players, divisions within the Workers’ Party, and the demands of interest groups. This explanation is discussed on the basis of Brazil’s negotiating position in WTO negotiations from 2003 to 2006.