This paper analyses the transformation of electoral cleavages in Brazil since 1989 using a novel assembly of electoral surveys. Brazilian political history since redemocratization is largely a history of the rise and fall of the Workers' Party (Partido dos Trabalhadores, PT). We show that the election of Lula da Silva as President in 2002, followed by the implementation of redistributive policies by successive PT governments, was at the origin of the marked socioeconomic cleavages that emerged. In a relatively short space of time the PT transformed itself from a party of the young, highly educated, high-income elite of the Southern party of the country, to a party of the poor and lesser educated voters, increasingly located in the disadvantaged region of the Northeast. Controlling for a host of socio-demographic factors, a voter in the Northeast was 20 percentage points more likely to vote for the PT in 2018 than voters in other regions, compared to being 5 percentage points less likely to do so in 1989. In sharp contrast to other western democracies, political conflict in Brazil has followed an increasingly unidimensional class-based path. This culminated in the unification of elites and large parts of the middle class behind Bolsonaro in the 2018 presidential election. We argue that contextual policy-driven factors and programmatic alliances are key to understand the PT's singular evolution, and thus the transformation of electoral cleavages in Brazil.