Australia end dismal T20 World Cup by thrashing Oman
Marsh reached his fifty inside the six-over power play and hit four sixes and seven fours in all as Australia, having bowled out Oman for 104, raced to 108-1 with more than 10 overs to spare.
Fellow opener Travis Head made 32 and Josh Inglis 12 not out but the win against a 20th-ranked Oman side will be scant consolation after a chaotic campaign in Sri Lanka.
A depleted Australia failed to make the second phase for only the second time in the event's history after defeats to Zimbabwe and co-hosts Sri Lanka.
"As I've said a few times, it's a bitterly disappointed change room," said Marsh.
"Like every team, we built towards this for two years. Unfortunately, in a couple of key games, we just didn't play our best cricket."
Australia arrived after being drubbed 3-0 in Pakistan and without injured fast bowlers Pat Cummins and Josh Hazlewood.
They then lost Marsh for the first two games after he was hit during practice and suffered testicular bleeding.
Australia's acerbic media did not hold back in their criticism after their fate was sealed when Zimbabwe's match against Ireland was washed out on Tuesday, citing selection "stuff-ups".
Chief among those was sticking with the woefully out-of-form Cameron Green and promoting Tim David to number four as a "power hitter" when he had not played since December because of a hamstring injury.
Glenn Maxwell, so often a match-winner with the bat in the past, struggled for runs and the Australians dearly missed the experience of Cummins and Hazlewood.
Matt Renshaw was Australia's top run scorer in the first two group matches, but he was bewilderingly dropped for the must-win Sri Lanka clash on Monday.
After Marsh won the toss and opted to bowl, Australia's Xavier Bartlett took a wicket with the first ball of the Oman innings, bowling Aamir Kaleem.
Bartlett took 2-27 and Adam Zampa 4-21 as Oman were routed for 104 in 16.2 overs with Wasim Ali top scoring on 32.
"It's been a really tough few days. There are some pretty quiet voices around the group right now," said Zampa, who was named player of the match.
"We're feeling flat about the World Cup ending so early for us
"I'm pretty disappointed overall. I'm certainly not ready to be flying home tomorrow."