In 2015, a center‐left government introduced an electoral reform that replaced the binomial electoral system governing parliamentary elections since 1989 with a more proportional system. This article provides an account of the reform process, describes the new electoral law, and discusses the factors explaining the reform. We argue, first, that it was possible, due to the incentives the government provided, to secure the support of an ample majority of parliamentarians; also, a new and favorable political scenario had emerged, in which the support of the main right‐wing parties was not necessary for the reform to pass. Second, we maintain that the reform sought mainly to resolve problems affecting the parties of the governing coalition related to negotiations of coalition lists for elections. As a complementary objective, the reform promoted a general interest by establishing rules that allowed a “fairer” system of representation and improved competitive conditions.