The Catholic Church in the four future counties composing the Diocese of Brownsville began in 1548, when the Spanish monarchy decreed, and Pope Paul III confirmed, the Diocese of Guadalajara. These mission lands, part of the northern provinces of New Spain, were within the jurisdiction of the Franciscan colleges for the Propagation of the Faith at Querétaro and Zacatecas. In 1777 the Diocese of Linares was formed; in 1792, when the see (episcopal seat) was moved, it became the Diocese of Monterrey. Subsequent church-state tensions in Mexico resulting from the decade-long Mexican war of independence left the Diocese of Monterrey with no resident bishop. The Mexican War also disrupted life in the lower Rio Grande area. However, there were scattered priests who ministered to Catholics on both sides of the Rio Grande (see CATHOLIC DIOCESAN CHURCH OF SPANISH AND MEXICAN TEXAS). With the establishment of the Prefecture Apostolic of Texas in 1840, the Brownsville region came under American administration.
The French-speaking Oblates of Mary Immaculate were the first order of religious to arrive in the lower Rio Grande region after the establishment of the Diocese of Galveston in 1847. They were recruited by Jean Marie Odin, its first bishop. Upon their arrival in 1849 they found most of the Catholics in the area living on ranchos. Thus began the horseback ministry of the Oblates at Santa Rita and more than 100 other ranchos and communities along the river. La Lomita ranch, south of the site of present-day Mission, became an important way-station for the "Cavalry of Christ" (see LA LOMITA MISSION). The Galveston diocese included the entire state of Texas. Odin's successor, Claude Marie Dubuis, found the area too large to administer as a unit and appealed to Rome for some division of the territory. The resulting Vicariate Apostolic of Brownsville, established in 1874 by act of Pope Pius IX, included the land between the Nueces River and the Rio Grande, an area that later became the dioceses of Corpus Christi and Brownsville. By the same act Immaculate Conception Church in Brownsville (built under the direction of the Oblates and completed in 1859) was selected as cathedral. Catholics in the area numbered between 30,000 and 40,000. Those who resided in the four counties that make up the present Diocese of Brownsville were mostly all Mexican Americans who could trace their lineage to early settlers brought by José de Escandón's colonization of the region in the mid-eighteenth century. Many of the oldest towns in the present diocese originated with these early Catholic settlements. Laredo was the oldest city in the vicariate and is the site of the oldest parish in South Texas, San Agustín, built in 1789. The first bishop of the vicariate was Dominic Manucy, a priest from the Diocese of Mobile. He had only about twenty priests: fourteen Oblates in Brownsville, Rio Grande City, and Roma, and others in Corpus Christi, Laredo, Refugio, San Patricio, and San Diego.
In 1875 Manucy moved the see to Corpus Christi, built a new church there to replace the original worn-out structure that had served the community since 1854, and kept the name of St. Patrick's for the new church, completed in 1881. When Manucy requested a transfer and was appointed bishop of the Diocese of Mobile in 1884, he appointed Father Claude C. Jaillet as vicar general of Brownsville. From 1885 to 1890 Jaillet handled the administration, and the vicariate had no bishop.
From 1852 on, the Oblates consistently accounted for half of the clergy in the vicariate. Notable orders of women serving in the vicariate were the Sisters of the Incarnate Word and Blessed Sacrament, who came from Lyons, France, and arrived in Brownsville in 1853; the Ursuline Sisters, who came to Laredo in 1868; and the Sisters of Mercy, who arrived in Refugio in 1875. The Brownsville convent and school of the IWBS sisters were demolished by the hurricane of 1867 but soon reconstructed. Peter Verdaguer, made second bishop in 1890, moved the see to Laredo, where most of the Catholic population lived. He was highly esteemed by the people, who affectionately called him "Padre Pedro." He continually traveled throughout the vicariate for the twenty years of his assignment, and died on a tour of confirmation near Mercedes in 1911. Provincial bishops meeting in New Orleans later that year requested that Rome elevate the vicariate to a diocese. Pope Pius X did so in 1912 and made Corpus Christi the see city. The following year Paul J. Nussbaum was named bishop. With an area of 88,000 square miles, the new diocese had a total population estimated at 158,000; 83,000 of these were Catholics, and 70,000 of these were Hispanic. Bishop Emmanuel B. Ledvina succeeded to the see in 1921. He became a great builder of churches in the diocese before resigning for reasons of health in 1949 and being succeeded by Mariano S. Garriga.
The Diocese of Brownsville was established on July 10, 1965, composed of four counties in the lower Rio Grande valley—Cameron, Hidalgo, Starr, and Willacy—an area of 4,226 square miles, taken from the Catholic Diocese of Corpus Christi. Its first bishop was Adolph Marx, who had been auxiliary bishop in Corpus Christi. Marx was installed in September 1965; he soon left for Europe to attend meetings of the Second Vatican Council, and died on November 1 in his birthplace, Cologne, Germany. His successor, Humberto Medeiros, was appointed and installed in 1966. Medeiros left Texas to become archbishop of Boston in 1970 and was made a cardinal in 1973. John J. Fitzpatrick served as bishop of Brownsville from 1971 until his retirement in 1991. An important feature of his tenure was attention to the migrant farmworkers of South Texas. In a 1977 publication, Fitzpatrick noted that "70 per cent of the 400,000 people in the Valley [were] Catholics; 83 per cent of the Catholics speak Spanish as their first language....Only 112 priests serve almost 300,000 Catholics, the lowest ratio of priests to Catholics in any diocese in this country." A 1976 survey of the diocese showed that 57 percent of the 61 parishes had Sunday Masses in Spanish. Of all Masses each week, 56 percent were in Spanish. Fitzpatrick was succeeded by Enrique San Pedro, a native of Cuba who had served five years as the first Hispanic auxiliary bishop of the Diocese of Galveston-Houston. San Pedro died in 1994, and Raymundo Peña was appointed to succeed him.
In 1994 the Catholic population of the diocese was 652,214 (of a total population of 805,203), served by sixty-one parishes and forty-six missions. Fifty-nine of the parishes had resident pastors. The diocese had two homes for the aged, two retreat houses, one health-care center, and nine social-service agencies. Men's religious orders represented in the diocese numbered ten; women's, thirty-six. There were seven monastery-residences for priests and brothers and sixty-six convent-residences for sisters. Catholic student centers were located at the campuses of the University of Texas at Brownsville and U.T–Pan American at Edinburgh. Catholic elementary and secondary schools enrolled 3,238 students.