Bradford opened their League Two campaign with a disappointing defeat at the Priestfield Stadium.
Phil Parkinson’s Bantams have long been tipped as promotion candidates from League Two, but they did not get off to an ideal start.
They went into the half-time break trailing 1-0 after Danny Kedwell gave the Gills a 43rd-minute lead.
And Kedwell doubled the Gills’ lead on 54 minutes from the penalty spot.
But Bradford’s Nekhi Wells gave the Bantams hope with a goal in the 64th minute.
Any hopes of a comeback, however, were quashed when Myles Weston sealed the points for Gillingham with a third goal in the 88th minute.
Gillingham: Nelson, Flanagan, Frampton, Fish, Martin, Lee, Montrose, Allen, Jackman, Burton, Kedwell. Subs: Forecast, Tayne, Strevens, Davies, Dack, Weston, Barrett.
Bradford: Duke, Oliver, Meredith, Darby, Reid, Thompson, Atkinson, Gary Jones, McArdle, Connell, Hanson. Subs: McLaughlin, Davies, Hannah, McHugh, Hines, Wells, Doyle.
Referee: Mick Russell (Hertfordshire)