Duke, 34, made 23 appearances for Hull City last season and is reported to have turned down Rochdale to join the Bantams. Duke has signed a two year deal. He played for Burton Albion 112 times scoring once and Hull City 50 times. While at Hull in January 2008 Duke had an operation to remove a testicular tumour.
Joining from Hull is winger Jamie Devitt who is on loan until January. 21, he joins City as the latest loan club following spells at Grimsby Town, Darlington and Shrewsbury Town.