It was a winner-takes-all Australian derby with both teams level on 40 points and needing to win to take their place in next week's top-six playoffs.
The Brumbies, twice winners of the southern hemisphere provincial championship, will have to wait until the result of the Highlanders' match on Saturday with the Crusaders to see whether they keep hold of fourth place and a home play-off next week.
The Highlanders must beat the Crusaders in Christchurch to deny the Brumbies fourth place.
Wallaby back Toomua was the hero of the Brumbies' bonus point win scoring three of his team's seven tries.
Other tries went to Jesse Mogg, Joe Tomane, Tom McVerry and impressive winger Henry Speight.
Christian Lealiifano kicked three conversions and two penalties.
It was the first time the Brumbies have won in the last round of Super Rugby since 2007.
Last year the Brumbies suffered a shock loss against the Force in Perth which cost them an all-important top-two finish.
The Brumbies' win was never in doubt and after leading 21-6 at halftime, the home side went on with the job winning the second half 26-19. They clinched their four-try bonus point just four minutes after the resumption.
It was the Brumbies' biggest win of the season and puts them in great heart for next week's play-off.
It was a sad end for the Force, who were bidding for their first Super Rugby finals campaign and they finished with three tries to Pek Cowan, Chris Tuatara-Morrison and Zack Holmes.
"To get a score like that in the final round when a finals spot is on the line is a really pleasing result," Brumbies skipper Ben Mowen said.
"I think we'll play the Highlanders next week, the Crusaders will be really strong at home but we'll sit back and wait and see."
Force captain Matt Hodgson said despite the loss it had been a great season for the Perth-based side.
"We've
learned how to win consistently and it's now just a case of learning
how to play those big games like tonight and we'll improve again next
year," he said.
Scorers
Brumbies - Tries: Matt Toomua (3), Jesse Mogg, Henry Speight, Joe Tomane, Tom McVerry. Conversions: Christian Lealiifano (3). Penalties: Lealiifano (2).
Force - Tries: Pek Cowan, Chris Tuatara-Morrison, Zack Holmes. Conversions: Jayden Hayward, Sias Ebersohn. Penalties: Hayward (2).
Teams:Brumbies
15 Jesse Mogg, 14 Henry Speight, 13 Tevita Kuridrani, 12 Christian Lealiifano, 10 Matt Toomua, 11 Clyde Rathbone, 9 Nic White, 8 Ben Mowen (captain), 7 Jarrad Butler, 6 Scott Fardy, 5 Leon Power, 4 Sam Carter, 3 Ben Alexander, 2 Josh Mann-Rea, 1 Scott Sio.
Substitutes: 16 Ruaidhri Murphy, 17 Ruan Smith, 18 JP Smith, 19 Fotu Auelua, 20 Tom McVerry, 21 Michael Dowsett, 22 Joe Tomane, 23 Pat McCabe.
Force
15 Jayden Hayward, 14 Dane Haylett-Petty, 13 Solomoni Rasolea, 12 Chris Tuatara-Morrison, 11 Nick Cummins, 10 Zack Holmes, 9 Ian Prior, 8 Ben McCalman, 7 Matt Hodgson (captain), 6 Brynard Stander, 5 Wilhelm Steenkamp, 4 Sam Wykes, 3 Kieran Longbottom, 2 Nathan Charles,1 Pek Cowan.
Substitutes: 16 Heath Tessmann, 17 Tetera Faulkner, 18 Oliver Hoskins, 19 Adam Coleman, 20 Chris Alcock, 21 Alby Mathewson, 22 Luke Burton, 23 Dillyn Leyds/Sias Ebersohn