By the end of the nineteenth century Catholicism had become a peripheral player in the international arena. This would change in the twentieth century as Catholicism would re-emerge as a formative participant in the creation of the Human Rights movement. To examine this question, Chapter 3 seeks to comprehend in what manner Catholicism began moving from the periphery to the centre of international law. The narrative begins to distinguish how Catholicism began drawing upon its own understanding of the natural law and the formation of the state, and explores in what manner the Catholic Church would shape democratic constitutions and international law across Europe. The Catholic Church’s engagement with the construction of human rights became a cosmopolitan vehicle to participation in the international legal system, which mapped out in a number of ways. This chapter concludes by ascertaining how this latter engagement provided the Catholic Church with theoretical underpinnings to further shape the direction of human rights, in its negotiation and engagement with a globalised world. It reveals how Catholic cosmopolitanism was understood as the political form of sovereignty.