Joe Tomlinson gave MK Dons an early lead, which was cancelled out by Alex Gilliead. Jack Payne restored the Dons’ lead before Max Dean and Alex Gilbey added second-half goals.
MK Dons got their first win in nine League Two games, while Bradford lost for the first time in four.
The Dons struck early when Payne’s low corner picked out Tomlinson, whose low strike from just outside the box beat Harry Lewis.
Gilbey, Dean and Tomlinson all came close to a second but Bradford then equalised as Gilliead beat Craig MacGillivray from outside the box.
The Dons re-took the lead just after half an hour as Payne’s free-kick from 25 yards flew past Lewis.
Dean then hit both post and bar, but he scored the Dons’ third when he steered home Tomlinson’s cross.
The hosts added a fourth late on as Gilbey took advantage of a defensive error to score.