Deas was born in Camden, South Carolina, a son of James Sutherland Deas and Margaret Rebecca (Chestnut) Deas. He was a cousin of future fellow Confederate general James Chestnut, Jr.. He was educated in South Carolina and in Caudebec, France. In 1835, his family moved to Mobile, Alabama, where he initially engaged in the mercantile business. He served in the army during the Mexican-American War. After the war, he became a prominent cotton broker in Alabama and amassed a significant fortune from his speculation. He married Helen Gaines Lyon on May 16, 1853.