St. Thomas High School is an all-boys, Catholic college preparatory school in Houston, Texas. Founded in 1900, St. Thomas is the second oldest continuously operating private high school in Houston behind Incarnate Word Academy, which was founded in 1873. The school is operated by the Basilian Fathers in the Archdiocese of Galveston-Houston.

The Congregation of St. Basil, also called the Basilians, is a Roman Catholic clerical religious congregation of Pontifical Right for men. It is an apostolic community whose members profess simple vows. The Basilians seek the glory of God, especially in the works of education and evangelization. The congregation was founded in 1822 in the aftermath of the French Revolution. In the early 19th century the Basilian Fathers' educational and pastoral work brought them to a variety of locations in Canada and the United States. In the 1960s, the priests began to minister in Mexico, and in Colombia in the 1980s.