Notably, Tucker was appointed to the law faculty at the College of William & Mary (1801-1804) and later was captain of Cavalry in the War of 1812. He was elected as a Republican to the U.S. House of Representatives and served for two terms, from 1815 to 1819. In 1823 he had a son, John Randolph Tucker. He went on to be judge and president of the Court of Appeals of Virginia (1831-1841) and then became a professor of law at the University of Virginia (1841 to 1845).
As a law professor, Tucker authored Tucker's Commentaries as well as several treatises on natural law and on the formation of the Constitution of the United States. He is also widely known for adding a mandatory pledge to the student honor code while a professor at the University of Virginia. On July 4, 1842, St. George Tucker offered the following resolution as a gesture of confidence in students: "...resolved, that in all future examinations ... each candidate shall attach to the written answers ... a certificate of the following words: I, A.B., do hereby certify on my honor that I have derived no assistance during the time of this examination from any source whatsoever." Tucker's pledge was adopted and soon became the following: "I do hereby certify on honor that I have derived no assistance during the time of this examination from any source whatever, whether oral, written or in print." This basic pledge has, in one form or another, been adopted at many American universities.
Tucker resigned in July, 1845 due to ill health. He died in Winchester, Virginia in 1848.