Leon Johnson's first goal of the season eased Gillingham's relegation worries.
On-loan Bradford defender Kelly Youga was sent off for two bookings and the Gills made their advantage count.
Johnson rose at the far post to power a Clint Easton corner past Donovan Ricketts after Bradford had earlier missed several good chances.
The Gills dominated possession in the second half but failed to make the most of their chances and with Matthew Jarvis' curling shot hitting the post.
Gillingham: Larrieu, Southall, Jackman, Chorley, Johnson, Bentley, Flynn, Crofts, Easton (McDonald 58), Mulligan (Ndumbu-Nsungu 46), Jarvi
Subs Not Used: Cox, Sancho, Collin.
Goals: Johnson 45.
Bradford: Ricketts, Edghill, Youga, Wetherall, Bower, Daley (Hibbert 78), Bridge-Wilkinson, Schumacher, Logan (Clarke 45), Dyer, Paynter (Johnson 58).
Subs Not Used: Howarth, Bentham.
Sent Off: Youga (42).
Booked: Youga, Johnson.Att: 5,513
Ref: A Hall (W Midlands).