Joe Daniher kicked four goals for the Lions on Thursday night, while Charlie Cameron booted three as Brisbane moved ahead of the Cats to third on the ladder with the 13.16 (94) to 7.8 (50) win.
Daniher and Cameron were ably supported by ex-Cat Lincoln McCarthy and Eric Hipwood, who kicked two goals each.
The victory is Brisbane's sixth straight win at the Gabba and only its second victory over the Cats since 2013, while the result ends Geelong's six-match winning run.