DeVane was in private practice in Tampa from 1908 to 1918. He was county attorney for Hillsborough County from 1913 to 1914 and counsel to the Florida Railroad Commission from 1918 to 1920. Rate attorney was rate attorney for AT&T from 1920 to 1922, and was associate and general counsel for Chesapeake and Potomac Telephone Co. from 1922 to 1930.
DeVane was in private practice in Washington, D.C., from 1930 to 1933, and solicitor for the Federal Power Commission in Washington from 1933 to 1938. He was in private practice in Orlando, Florida, from 1938 to 1943.
President Franklin D. Roosevelt nominated DeVane to the United States District Court for the Southern District of Florida and United States District Court for the Northern District of Florida on March 26, 1943, to a seat vacated by Curtis L. Waller. Confirmed by the Senate on April 14, 1943, he received commission on April 22, 1943.
On the court DeVane earned a reputation as a "staunch segregationist.
DeVane assumed senior status on January 31, 1958 and remained on the court until his death in 1963.