He was born in Marksville, Louisiana, youngest son of Judge Thomas Overton and Elizabeth Waddill Overton, graduated from Louisiana State University in 1895, from Tulane University in 1897, and was admitted to the Louisiana bar in the following year.
He then set up his practice in Alexandria. In 1905 he married Ada Ruth Dismukes, and they had two daughters, Katherine and Ruth.
He entered Congress by appointment, to fill the vacancy caused by the death of representative James B. Aswell, and served from May 12, 1931, to March 3, 1933. In 1932, he ran for the Senate and won.
He was reelected in 1938 and 1944. His committee memberships included Manufactures, Commerce, and Irrigation and Reclamation.
He was a traditional segregationist; he opposed an amendment to the Selective Service Act of 1940 that allowed the voluntary enlistment of minorities, on the grounds that it could lead to mixed units, and was quoted in 1947 as saying "The Democratic South stands for White supremacy".
Overton's last term was cut short by his death at Bethesda Naval Hospital. His remains were buried at Mount Olivet Cemetery in Pineville, Louisiana. His house in Alexandria was added to the National Register of Historic Places in 1985.