Born in Lowndesville, South Carolina, Mann attended the common schools and was graduated from The Citadel, Charleston, South Carolina, in 1901.

He graduated from the law department of the University of South Carolina at Columbia in 1906, where he was a member of the Euphradian Society, and commenced practice in St. Matthews, Calhoun County, South Carolina.

Mann was elected as a Democrat to the 66th Congress to fill the vacancy caused by the resignation of Asbury Francis Lever and served from October 7, 1919, to March 3, 1921.

He was appointed master in equity for Orangeburg County in November 1923.

He was interred in Sunnyside Cemetery, Orangeburg, South Carolina.