A week after coming from 44 points down to beat GWS, the Lions erased a 25-point third-quarter deficit in their 14.11 (95) to 12.13 (85) preliminary final victory at the MCG on Saturday.
Chris Fagan's side will meet Sydney on September 28 in the first grand final featuring two non-Victorian clubs since 2006.
It will be Brisbane's second successive grand final appearance, following a heartbreaking four-point defeat to Collingwood last year.
The Lions, who finished fifth on the ladder, could become just the second team to win the premiership from outside the top four under the current finals system, introduced in 2000.
Geelong, meanwhile, will rue another missed opportunity after losing a preliminary final for the sixth time in Chris Scott's 14-year coaching tenure.
The Cats lost Max Holmes to another hamstring injury, two years after the speedster missed the 2022 premiership with a minor strain.
Captain Patrick Dangerfield would also have been in doubt for the grand final if Geelong had qualified, facing scrutiny over a dangerous tackle on Hugh McCluggage.
Instead it is McInerney who shapes as Brisbane's heartbreak story after hurting his left shoulder late in the first quarter.
Oscar McInerney (centre) suffered a shoulder injury and is in doubt for the grand final. (Joel Carrett/AAP PHOTOS)
The ruck star carried on bravely, but was substituted out of the game during the third quarter and taken to hospital.
Lions co-captain Lachie Neale was huge for his side with 31 disposals and 12 clearances, lifting during the third quarter with the game on the line.
Geelong led by 25 points soon after half-time, but Brisbane kicked seven of the next eight goals and prevailed in a gripping finish.
Callum Ah Chee kicked three goals for the Lions, including two crucial majors in the final term.
His snap with less than three minutes left gave Brisbane the lead for the last time, before Cam Rayner sealed the result with a left-foot shot on the run.
A goal on the run from Brisbane's Cam Rayner (centre) sealed victory over the Cats. (Joel Carrett/AAP PHOTOS)
Joe Daniher was also important for the Lions, stepping into the ruck when McInerney went down, as were Dayne Zorko (32 disposals), Josh Dunkley (28) and McCluggage (27).
Rayner, Logan Morris, Charlie Cameron and Zac Bailey kicked two goals apiece.
Geelong had kicked seven goals to two in the second quarter, with Ollie Henry (four goals) and Gryan Miers (two) at the heart of their scoring, contributing four majors and two goal assists between them for the term.
The pair connected in spectacular soccer-style fashion when Miers' dribbled pass off the ground from the boundary was tapped in by Henry on the goal line.
Ollie Henry (left), marking in front of Dayne Zorko, kicked four goals for the Cats. (Joel Carrett/AAP PHOTOS)
Miers added another with a floating snap from the other pocket, and the Cats took a 19-point lead to the main break.
Zorko gifted Geelong the first goal of the second half, but the Lions returned fire and led by two points at the final change.
In a tense finish, Tom Stewart laid a season-saving tackle on Zac Bailey at one end to allow Ollie Henry (four goals) to put the Cats in front at the other with less than three minutes on the clock.
But Ah Chee's snap wrested back the lead for Brisbane and Rayner struck again, before Jack Payne laid a desperate tackle on Mitch Duncan to help see the Lions home.
It was Brisbane's first win over Geelong in Victoria since the 2004 preliminary final.
