Catholic backlash against the liberalization of abortion and same-sex marriage laws in the Americas has been gathering momentum through the use of constitutional and human rights arguments. While Bishops’ Conferences as well as individual priests and the Vatican itself continue to frame sexual and reproductive rights in the language of God and faith, lay Catholic lawyers have translated theology into constitutional and human rights arguments to halt and reverse liberal abortion and same-sex marriage laws. Their arguments invoke reason instead of faith, based on the claim that the right use of reason in legal arguments leads to the same conclusions as theological reasoning. This article examines the main arguments recently used by lay Catholic lawyers in the United States, Colombia, Mexico, and Brazil and relates them back to the Vatican’s position on human life, religious freedom, and gender equality. This article examines these parallels, their implicit theological basis, as well as their tensions, both rhetorical and substantive, with mainstream constitutionalism.