Chasing 173 for victory, Marsh was the hero for Australia on Sunday as he muscled an unbeaten 77 from 50 balls to set up the win with seven balls to spare.
David Warner, who also hit 53 from 38 as part of a 92-run second-wicket stand with Marsh, was named player of the tournament after entering it with questions over his own form.
It helped end a 14-year wait for Australia to claim the one trophy that has eluded them.
“I just wanted to get out there and have a presence,” Marsh said.
“What an amazing six weeks … World Champs.”
Yet at times, as Kane Williamson was smashing them for 85 from 48 balls, the trophy looked some way off for Australia.
And when captain Aaron Finch fell early, Australia needed a man to stand up in the chase.
Enter Marsh, who produced his finest hour as an Australian cricketer to be crowned man of the match in a World Cup final.
He put Adam Milne into the crowd at backward square the first ball he faced, and sent the next two deliveries to the boundary.
He made a clear statement of force against each of the Black Caps’ bowlers, dispatching Jimmy Neesham and Mitch Santner for six off the first balls they bowled.
The right-hander also took another Ish Sodhi over for 16, as the legspinner lost his way and the game got away from New Zealand.
Out of the picture in international cricket months ago and after only playing 15 T20s for Australia in the 10 years before 2021, the tournament has been a coming of age for Marsh.
The West Australian averaged 61.66 in the UAE at a strike-rate of above 145, while his year is now the most prolific of any Australian in the T20 format.
He finished Sunday night with 10 boundaries – including four sixes – as Australia made light work of the biggest chase in T20 World Cup final history.
Australia’s triumph came after they entered the tournament as rank outsiders, after five straight series losses.
But by the time Glenn Maxwell (28 from 18) produced a switch hit to finish the job, they were on top of the T20 world for the first time.
“This is huge,” captain Aaron Finch said.
“To be the first Australian team to be able to do it. So proud of the way the guys went about the whole campaign.”
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