Born: December 3, 1834, Poughkeepsie, New York.
Died: July 2, 1918, Elizabeth, New Jersey.
Buried: Evergreen Cemetery, Hillside, New Jersey.
Thomas was the son of William Vassar and Mary Hageman, and husband of Tamma Guernsey Sackett (married 1861). He was a descendant of Matthew Vassar, founder of Vassar College, and nephew of evangelist John Vassar.
Vassar was ordained a Baptist minister in 1857. During the American civil war, he was chaplain of the 150th New York Volunteer Infantry, and was at the Battle of Gettysburg.
He held pastorates at the South Baptist Church, Newark, New Jersey, and congregations in Amenia, New York; Lynn, Massachusetts; Flemington, New Jersey; and Kansas City.
He served as president of the New Jersey Baptist Sunday School Union.