This dissertation examines the Catholic Church’s response to the mid-nineteenth century Mexican liberal Reforma through a study of the life and work of Bishop Clemente de Jesús Munguía (1810-1868), one of the most influential yet least-known ecclesiastical intellectuals of the period. A lawyer by profession, Clemente Munguía was first professor and then rector of the Morelia diocesan seminary, where he undertook a major reform of the school’s curriculum and also composed several textbooks on a variety of subjects, including grammar, literature, rhetoric, philosophy, theology, and law. Appointed Bishop of Michoacán in October 1850, Munguía distinguished himself for his staunch opposition to the state’s encroachment on the Church, as well as for his insistence on the need for religious intolerance in what he imagined as an “exclusively Catholic” nation. His protests against the 1857 Constitution and the liberal legislation enacted by President Ignacio Comonfort were a key factor in the outbreak of the Civil War of the Reform (1858-1860) and the subsequent French intervention (1862-1867), which resulted in the separation of Church and state and the collapse of Mexican conservatism. Unlike previous studies, this dissertation argues that Bishop Munguía’s opposition to the Reforma derived not from a blind “reactionary” intransigence, but instead from his desire to emancipate the Church from the subordinate status it had under the colonial ancien régime. Far from the stereotype of a backward and parochial intellectual, Munguía was a sophisticated scholar who sought to reconcile Catholicism with the larger currents of thought of the Atlantic Republic of letters. Indeed, he believed that the liberal revolution should be countered “with its own weapons,” a conviction which first led him to frame the defense of ecclesiastical prerogatives in the language of modern natural law, and then to claim for the Church the very power of constitutional interpretation. Although Munguía’s ideal of a “Catholic republic” became unfeasible after the liberals’ final victory in 1867, his efforts at consolidating ecclesiastical independence paved the way for both the Romanization and the social activism that characterized the Mexican Church during the latter half of the nineteenth century. / text