On a day of utter madness at GIO Stadium, Brisbane halfback Ben Hunt nailed a golden-point field goal in the 94th minute to send the Broncos to a preliminary final.
They will face either Canterbury or Penrith in a fortnight at Suncorp Stadium, while minor-premiers Canberra must do it the hard way against Cronulla next Saturday night.
But the story of Sunday was Walsh, who was sin-binned for headbutting Hudson Young in the second half before producing one of the greatest seven-minute stints seen in a final.
Fresh off flipping the bird to the crowd on the way off the field, Walsh returned from the sin bin to lead the Broncos back from 28-12 down at the 66-minute mark.
The Broncos star first went 40 metres to score a try of his own, set up a second with a pass for Jordan Karapani, then kicked a crucial 40-20 in the lead-up to another.
With Brisbane down 28-26 Walsh then had a two-point field goal shot hit the cross bar, before Zac Hosking took out the fullback's leg as he attempted another one.
That gifted the Broncos a penalty on the full-time siren for Walsh to make it 28-28, before a 10-minute extra-time period where neither team could break the deadlock.
With the match in golden point, Canberra thought they had it won when Jamal Fogarty crossed, only for the bunker to spot a Jed Stuart knock-on in the lead up.
From the next set, Brisbane went downfield and Hunt nailed a field goal from 38 metres out to seal the match and begin to put the demons of the 2015 grand final behind him.
But questions will remain over whether Walsh should have even been on the field to produce the heroics.
Upset by a Young celebration, Walsh pushed his head into the Canberra second-rower's forehead before both were sin-binned and Brisbane awarded a penalty.
"Well, they've set a precedent now - you're allowed to headbutt," Canberra coach Stuart said afterwards.
"If Joe (Tapine) or Hudson had have used their head on Reece Walsh, what do you think would have happened to them?
"I don't know how they got the penalty to be honest.
"They got it 100 per cent wrong, but we shouldn't make it about that because it was an unbelievable promotion of the game itself."
Brisbane coach Michael Maguire said in his post-match press conference that he needed to look at the incident again, but suggested Walsh and Young were having "more of a conversation".
With Walsh in the bin Brisbane looked set to unravel, as Broncos captain Pat Carrigan followed his fullback to the sidelines for a shoulder charge on Morgan Smithies.
With that pair off, Canberra looked certain to run away with the match courtesy of fullback Kaeo Weekes.
After already helping Canberra to an 18-12 halftime lead just before the break, Weekes appeared to put one nail in Brisbane's coffin when he picked up a loose ball and went 95 metres to score.
And when Ethan Strange stepped Brisbane's 11-man defence soon afterwards to make it 28-12, the Raiders looked home.
But no one could have predicted what would come next, with Walsh going from zero to hero and Brisbane claiming one of the most epic finals wins of all time.
"His maturity and what I have seen over the last four or five months, I think he has been working towards that," Maguire said.Â
"He knows that. There is a lot of talk around Reecey but he knows what he is capable of and the boys get around him and back him."
Beyond judiciary dramas, Brisbane will also sweat on a left ankle injury suffered by Payne Haas, who battled on to finish the match.
There were also fears second-rower Brendan Piakura suffered a depressed cheekbone.
