From 1921 to 1932, Mills taught school in Mer Rouge in Morehouse Parish. He was the Louisiana supervisor of public accounts from 1933 to 1936. He was also engaged in agricultural pursuits, cattle raising, real estate, and oil. In 1936, he served as colonel on the staff of the governor.
Congress
Mills was elected as a Democrat to the Seventy-fifty, Seventy-sixth, and Seventy-seventh Congresses from January 3, 1937, to January 3, 1943. He unseated Representative Riley J. Wilson of Catahoula Parish in the 1936 Democratic primary. In 1942, however, he was himself defeated for renomination by Charles E. McKenzie, a native of DeSoto Parish who had relocated to Monroe.
Mills resumed his involvement in oil and natural gas, cotton planting, and a building-supply company. He was a resident of Monroe until his death there at the age of ninety-six on May 15, 1996.