The Shakers claimed their second home win in four days after Andy Morrell scored for the second successive game, grabbing a deserved winner in the 76th minute.
Bury made a lively start and Bradford keeper Rhys Evans had to be alert to save low to his left after Andy Morrell deflected Elliott Bennett's right-wing cross goalwards.
Matthew Clarke then did well to head clear after a deft cross by Bury's top scorer Andy Bishop, who signed a new three-and-a-half year deal earlier in the day.
Barry Conlon replaced Peter Thorne up front for Bradford and headed well wide from a Nicky Law corner, before the two sides became locked in a battle for midfield supremacy.
Despite some neat football from both sides, neither managed to forge an opening until Bury winger Mike Jones dragged a shot wide from Bishop's lay-off on the half-hour mark.
Bishop then picked out Morrell with a searching cross-field ball, only for his strike partner to volley over from a tight angle.
Conlon sent an attempted lob well over after a well-timed tackle by strike partner Steve Jones before Bury almost snatched a half-time lead.
Evans had to turn wide a fierce effort from Mike Jones, while Paul McClaren blazed over from Bradford's first decent chance.
Bury again started the half strongly - Morrell heading wide from a Brian Barry-Murphy cross and Bishop denied by Evans after being put through by Bennett.
Bradford replied with Law firing straight at Mark Tyler after some uncertainty in the Bury defence.
But Bury continued to push forward, Morrell this time heading wide from a Mike Jones centre before finding the target with time running out.
Bishop found Morrell on the left and Graeme Lee stood off the veteran striker, allowing him to fire inside the near post.
Conlon and sub Michael Boulding went close late on but Bury held on.