He was raised in Beverley, where his father was an early settler and served as the town's mayor for a period.
Mann enlisted in the Australian Imperial Force in December 1914, and during the war served with the 10th Light Horse Regiment.
[1] Mann first ran for parliament at the 1924 state election, but was narrowly defeated by Charles Wansbrough in the seat of Beverley, losing by just 15 votes on the two-candidate-preferred count.
He had switched back to the Country Party by the 1930 election, and on his third attempt defeated Wansbrough with 55.4 percent of the two-candidate-preferred vote.
He held that seat until his retirement at the 1962 election, consistently winning large majorities (and running unopposed on one occasion, in 1953).