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.

During his tenure, Tucker was a supporter of the American System, including the establishment of the Second Bank of the United States and the passage of the Tariff of 1816.

He is 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.