Thomas Welles Bartley (also known as Thomas W. Bartley) (February 11, 1812 - June 20, 1885) was a Democratic politician from Ohio. He served as the 18th Governor of Ohio. Bartley was succeded in office by his father, Mordecai Bartley, one of only a few instances of this occurring in high elected office in the United States.

Bartley was born in Jefferson County, Ohio. After attending Jefferson College , Bartley began practicing law in 1831. He served in the Ohio House of Representatives from 1839-1841 and then in the Ohio State Senate from 1841-1845. He was elected Speaker of the Senate in 1843. When Wilson Shannon resigned as Governor on April 15, 1844, to take a diplomatic appointment, Bartley became Governor while concurrently remaining in the Senate. He served out the remainder of Shannon's term until December 3. Bartley sought renomination under the Democratic Party, but lost at the state convention by a single vote - avoiding a contest against his father, who accepted the Whig nomination. Bartley later served a contentious term on the State Supreme Court from 1852-1859.