In a decider for the ages at Accor Stadium, the Broncos came from 22-12 down at halftime to stun the Storm and claim their first premiership since 2006.
Brisbane completed the comeback without Adam Reynolds who limped off in the second half, before halves partner Ben Hunt also suffered a concussion with eight minutes left.
Ezra Mam stepped up for the Broncos with a try assist and big defensive play swinging the match, after a year where he has dominated headlines.Â
But ultimately it was Walsh who was the hero, with his electric attack outdoing a superb first half from Melbourne's all-star big four.
The Brisbane star beat five men to score a superb first-half try, set up three others and produced three try-saving plays to take the Broncos to their seventh premiership.
The fullback's outing was a fitting end to a finals series he has dominated, saving Brisbane against both Canberra and Penrith.
But as good as Walsh's finish was in the 94-minute epic against the Raiders earlier this month, Sunday night was something special.
With Brisbane trailing by 10 at the break, Walsh kept the Broncos in the match when he first scrambled to stop Tui Kamikamica getting a ball down.
From the next set Mam stood up, sending Gehamat Shibasaki over on the left edge and breathing life back into the game.
Walsh then unleashed three minutes of attacking brilliance, with his quick hands first sending Deine Mariner over with a cut-out ball to make it a two-point game.
And with 23 minutes left Brisbane had the lead when Walsh got the ball, accelerated and threw another cut-out ball for Shibasaki to grab his second.
Then with Melbourne fighting to take back the lead, Walsh produced two more try-saving plays to keep the Broncos on top.
The fullback first chased down opposite number Ryan Papenhuyzen when he broke from a scrum, before another last-line-of-defence tackle on the Storm No.1 in the dying minutes.
Brisbane's efforts to hold on came after they capitulated in similar circumstances two years ago against Penrith, when 10 of the same players gave up a 16-point lead in the decider.
Earlier, Walsh was the one shining light for Brisbane in a first half dominated by Melbourne.
The No.1 laid on the fastest grand-final try of the NRL era when he burst onto a ball in the fourth minute, bust through Jack Howarth and sent a cut-out ball Deine Mariner's way.
But the next 15 minutes were all Melbourne, as the Storm shot to a 16-6 lead off the back of Harry Grant, Cameron Munster, Jahrome Hughes and Ryan Papenhuyzen.
The quartet all combined to send Nick Meaney over for the Storm's first, before Hughes grubber-kicked for Eliesa Katoa to get Melbourne's second.
Katoa then turned provider for the Storm's next, with a long cut-out ball for winger Will Warbrick to score, before Walsh's superb six-pointer made it 16-12.
But when Hughes stepped off his right twice to beat Brisbane's defence and score just before the break, Melbourne led 22-12 and appeared premiers in waiting.
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