The arrival of Luiz Inácio ‘Lula’ da Silva and the Partido dos Trabalhadores (Workers' Party, PT) at the helm of the Brazilian federal government in 2003 represented the culmination of a slow and deep-rooted process of party transformation. Attributable partly to the inevitable consequences of the party gradually inserting itself into governmental institutions, and partly to strategic decisions made by the dominant coalition that had controlled the PT since 1995, these transformations significantly changed the organisational features of the party, paving its way to the federal government. This article analyses these processes, and the subsequent changes throughout the Lula government, from an organisational perspective, linking exogenous challenges and the party's genetic model with the strategies consciously adopted by the petista leadership.