Born in Sandusky, Ohio, he fought at Gettysburg under George Armstrong Custer, developed the Mann Boudoir Car, a railroad sleeping car, and published the Mobile Register, The Smart Set, and Town Topics.
During the Civil War, Mann enlisted in the 1st Michigan Cavalry and was elected as a captain. He later became the lieutenant colonel of the 5th Michigan Cavalry. Then, in the late summer of 1862, he raised and organized the 7th Michigan Cavalry and was promoted to its colonel on February 9, 1863.
Following the war, he was a member of the Military Order of the Loyal Legion of the United States. The Swiss-born American artist Adolfo Müller-Ury (1862-1947) began a portrait of Mann in the middle of October 1902. When finished, Town Topics, November 27, 1902 commented favourably on the portrait of its proprietor: ‘...Mr. Ury’s friends will be pleased to note that his work has broadened a great deal in recent months. His portrait of Colonel Mann, particularly, is rendered with considerable freedom and vigor, and in this respect is the best work that the artist has produced. The portrait is fair in color, a good likeness - although the mouth is perhaps unnecessarily severe - and the downy quality of the white hair and beard is especially well painted...’ It was exhibited at the Noe Art Galleries, 368 Fifth Avenue, New York, January 5-19, 1903. The picture was inherited by Mann's daughter Emma, but is now lost.