We use variation in religious doctrine produced by the unexpected Second Vatican Council (1962–65) to investigate the impact of religion on democratization. The Council, which transformed the Catholic Church from defender of the ancien régime into a leading apostle of religious freedom, human rights and democracy, represents the most significant example of institutionalized religious change since the Protestant Reformation. We adopt a difference-in-difference approach to estimate the Council's impact on democracy. Furthermore, we provide historical narratives on how the post-conciliar Catholic Church influenced the democratization process in different national contexts. Our research substantiates that the Church played a decisive role in third wave democratization.