Martin Thomas McMahon (March 21, 1838 – April 21, 1906) was an American jurist and a Union Army officer during the American Civil War. He was awarded the United States military's highest decoration, the Medal of Honor, for his actions at the Battle of White Oak Swamp. After the war, he held various legal and judicial positions in the state of New York. He briefly served as the Minister Resident to Paraguay and was a New York State Senator for four years.