This dissertation leverages a phenomenon of racial reclassification in Brazil to shed new light on the processes of identity politicization. Conventional wisdom tells us that the history of race mixture, fluid racial boundaries, and stigmatized blackness lead Brazilians to capitalize on racial fluidity and change their racial identifications—to reclassify—toward whiteness. In more recent years, however, Brazilians have demonstrated a marked and newfound tendency to reclassify towards blackness. I argue that this sudden reversal is the unintended consequence of expanded access to secondary and university education in recent decades, which has led many to develop a racialized political consciousness, what I refer to as political identity. State-led efforts to better include lower-class sectors of the citizenry through educational expansion have increased formerly marginal and newly mobile citizens’ exposure to information, social networks, and the labor market, while also endowing them with greater internal efficacy. Greater exposure and efficacy, in turn, have led many to challenge commonsense racial hierarchies and the national myth of racial unity as they have come face-to-face with racialized inequalities in their quests for upward mobility. Reclassification toward blackness, then, is an articulation of these newfound and racialized political identities. This theory is informed and developed through in-depth interviews with reclassifiers collected during more than 15 months of field research in two Brazilian cities. These insights are empirically and systematically tested with longitudinal cohort analysis of annual household data from the census bureau. Additionally, drawing on original survey experiments and an original panel dataset of public university students, I test and find inconsistent support for a rival instrumental hypothesis based on the implementation of race-targeted affirmative action, as well as the hypothesis that racial identification has been shaped by the state’s changing discourse toward race and the national myth of racial unity. Finally, analyzing an originally designed survey, I explore the consequences of these racialized political identities for political engagement and the exercise of citizenship. Ultimately, this dissertation contributes a novel account of identity politicization at the individual level and emphasizes the interaction between social structure and citizenship institutions in these processes.