Armistead Thomson Mason (August 4, 1787 - February 6, 1819), the son of Stevens Thomson Mason, was a U.S. Senator from Virginia from 1816-1817. He was born at the 'Armisteads,' in Louisa County, Virginia, graduated from the College of William and Mary in 1807 and engaged in agricultural pursuits until he became colonel of Virginia Volunteers in the War of 1812 and subsequently brigadier general of Virginia Militia.
He was elected as a Republican to the United States Senate to fill the vacancy caused by the resignation of William Branch Giles and served from January 3, 1816 to March 3, 1817. He then moved to Loudoun County, Virginia and was an unsuccessful candidate for election in 1816 to the Fifteenth Congress in a campaign of much bitterness, which gave rise to several duels, and later resulted in his being killed in a duel with his brother-in-law, John Mason McCarty, at Bladensburg Duelling Field, Maryland, near Washington, DC. He is buried in the churchyard of the Episcopal Church at Leesburg, Virginia.