Hans Kelsen was one of the most important legal thinkers of the 20th century, and he is known for mounting an elaborate defense of liberal party democracy at a time when the latter was hardly the most popular form of regime. This article examines how Kelsen responded to two major political movements he experienced in his intellectual prime: political Catholicism, which he was confronted with in interwar Austria, and Christian Democracy, which became a hegemonic political force in Western Europe after World War II, when Kelsen was already in exile. The article reconstructs Kelsen's complex critique of these two religious movements and ends by reflecting on what we can learn from his arguments about current attempts to revive Christian political thought.