Thomas was born on the 2nd of April, 1871, in Waterford, Ireland, and he enlisted in the US Marine Corps while in Boston in May of 1893. He was a Corporal when he was attached to the Eighth Army Corps and it was his actions when he was deployed to Luzon that would earn him the Medal of Honor. The citation reads:

For distinguished conduct in the presence of the enemy in battle, while with the 8th Army Corps on 25, 27, 29 March, and 5 April 1899.

Thomas was one of five Marines to receive the Medal of Honor during the Philippine-American War and he received it on the 19th of July, 1901. He reached the rank of Sergeant before leaving the Marine Corps in July of 1907. Thomas Francis Pendegrast died on the 26th of April, 1913, at the age of 42. While his citation spells his name Prendergast, he is buried in the Greenwood Cemetery in Philadelphia, Pennsylvania, Section J, Division I, Lot 247, and his headstone shows his name spelled Pendegrast.