The influence of corporate money in politics is one of the most studied topics in political science in the U.S., although not so much so in recent democracies. Using new and public data from Brazilian elections, this dissertation investigates the process of institutional change that culminated in a 2015 decision by the Brazilian Supreme Court to ban corporate donations as a legal source of financing to politicians and parties. The episode exemplifies the worldwide tendency of judicialization of politics and fits the pattern of change identified by the literature as a critical juncture, understood as a relatively short period of time in which there is a heightened probability that agents' choices will affect the outcome of interest. Under exceptional circumstances of political and economic crisis, actors not institutionally in charge of law making set in motion a process of legislative change whose final outcome was not a faithful reflection of their preferences, but was deeply influenced by contingent elements. Public support in a context of severe revelations of corruption schemes explain how the Supreme Court was able to rule against the immediate interest of politicians and how the latter, having adjusted to find additional sources of money, were unwilling to reinstate corporate donation as a legal means of campaign financing. Having confirmed in Chapter two that incumbency is associated in Brazil with a negative effect on the electoral performance of office holders while the use of corporate money by candidates is legal, the dissertation examines the effects of the Supreme Court decision on municipal elections held after it came into effect. We investigate whether removing this important source of funding for both incumbents and challengers swings the balance in favor of office holders in both majority and proportional elections held in 2016. We find evidence that the ban on corporate donations favored incumbent mayors, suggesting that the historic decision, instead of levelling the playing field between incumbents and challengers, in reality helped office holders to win an additional term. It was not immediately visible due to the particular conditions in which the 2016 elections took place, when voters were particularly angry at incumbents due to the widespread news of corruption involving party officials. These findings indicate that, despite its intention to make Brazilian elections more competitive and open, the historic Supreme Court decision might have had the exact opposite effect, helping perpetuate in power politicians already in office.