The purpose of St. Mary's University is to be a community of faith committed to an educational venture that includes a dedication to scholarship and to service to the community. For forty years after the Marianists arrived in Texas in 1852, their educational efforts were directed toward serving the primary-school children in San Antonio at St. Mary's Institute and San Fernando Cathedral School. St. Mary's had both day students and boarders. As the latter group outgrew even subsequent buildings, it became necessary to move the boarders to newly built St. Louis College in West Heights in 1894. The institute had a high school known as St. Mary's Academy and a college division which three years later was authorized by the state of Texas to give degrees for higher studies. At first utilizing the physical facilities of both the downtown and the West Heights locations, the college prospered so well that it was necessary to add new buildings in 1908 and 1921. By 1923 the high school and college divisions were so large that it became impossible for them to continue sharing facilities, and the college division was moved to the St. Louis College site, where it was reorganized into schools of arts and sciences and business and became known as St. Mary's University. Evening and summer coeducational classes were started. In the same year the alumni of the downtown St. Mary's College decided to help the Marianists' work by building a much-needed gymnasium. It was completed two years later and is still known as Alumni Gym, home court of the St. Mary's Rattlers, perennial champions of the Big State Conference, an affiliate of the National Association of Intercollegiate Athletics. The alumni likewise continued a tradition begun in 1917 of having an oyster bake each year as a reunion activity. The event is now officially part of Fiesta San Antonio.
In 1934 a law school was incorporated into the university, and graduate studies began in 1936. In 1949 the Centennial Memorial Library, constructed almost entirely by students and faculty, was dedicated. Two years later Garni Hall for science and Charles Francis Hall, a dormitory, were built. During the 1960s four residence halls, a math and engineering building, a life-sciences building, a new law-school complex, and a new academic library (which contains 190,000 volumes) were added to the campus. The library special-collections division houses originals and copies of many documents, including the Spanish Archives of Laredo. The university became completely coeducational in 1963 and added a division of engineering in 1967. In 1974 the former library was remodeled into a student center. St. Mary's added five more dormitory buildings after 1980, as well as a business and administration building, a new law library housing 200,000 volumes, and a new University Center. V. J. Keefe Field on campus serves as baseball home field for the St. Mary's Rattlers and for the San Antonio Dodgers, a professional team of the Texas League. St. Mary's University presidents have been: Rev. Robert Mayl (1923–27), Rev. Alfred Rabe (1927–38), Rev. Walter Golatka (1938–47), Rev. Louis Blume (1947–53, 1963–73), Rev. Walter Buehler (1953–61), Rev. Charles Neumann (1961–63), Rev. James Young (1973–81), Rev. David Paul (1981–85), Rev. John A. Leies (1985–88), Rev. John Moder (1988–2000), and Charles L. Cotrell (2000-), the first lay president in the university's history. In the fall of 1999 the faculty numbered 193. St. Mary's had 4,137 students in the fall of 2000, of whom 2,331 were undergraduates.