Career
He was the son of Briggs Priestley (1821–1907), a Thornton-born millhand who became a major mill-owner in Bradford, Mayor of Bradford for 1877-1878 and Member of Parliament for neighbouring Pudsey from 1906 to 1918. William Priestley was also elected as Mayor of Bradford for 1904-1905. He was elected as Member of Parliament for Parliament in the 1906 general election, having failed to unseat Bradford East"s Conservative Member of Parliament in the 1900 general election.
He held the seat until his defeat at the 1918 general election.