Stuck on a last-chance train-and-trial deal with Brisbane in November, Shibasaki was one of seven debutants in Kevin Walters' 24-man squad named on Monday.
Broncos teammate Reece Walsh has also been named for his first tour, and could take the No.1 jersey off Dylan Edwards after his incredible Clive Churchill Medal performance on Sunday.
Blayke Brailey, Keaon Koloamatangi, Mark Nawaqanitawase, Jacob Preston and Ethan Strange are the other fresh faces in the squad captained by Isaah Yeo.
But it is Shibasaki who stands out most, rewarded for the Broncos' drought-breaking premiership by being selected ahead of Bradman Best in the squad.
"He'd had one crack at the NRL and lost his way a little bit, but he's had a second chance and made the most of it,'' Walters said on Monday.
"We saw him play outstanding football in the State of Origin series, and then in the Broncos' run in the past six weeks he has been one of their go-to players.
"Last night, to have two tries in a grand final, he has virtually forced his way into the squad."
Zac Lomax was another notable inclusion, amid speculation he will attempt to be released from Parramatta to join rebel rugby competition R360.
Walters said he had spoken to Lomax and was confident his focus would be on the tour, ahead of the first Test at Wembley on October 25.
"Having spoken to Zac himself, he certainly has a good mindset around the tour," Walters said.
"I have had several conversations with him, he is right to go."
ARL Commission chairman Peter V'landys again insisted he was not concerned about the breakaway competition becoming a distraction during the tour.
"Any competition that comes out of a corn-flakes box, I am not concerned about," V'landys said.
"Because that's what it is - it is (completely) unprofessional. They have no business plan. Any player that goes is risking their career.
"They only have to look at Salford this year in the Super League, it was a situation where players didn't get paid."
Walters has also been able to pick Tino Fa'asuamaleaui, Kotoni Staggs and Koloamatangi, after the trio each opted to play for Australia over Pacific nations.
Keeping them in the Kangaroos jersey for next year's World Cup will likely loom as crucial for officials, with players able to decide their allegiance again next season.
Fa'asuamaleaui and Staggs last played for Australia in the 2023 Pacific Cup final loss to New Zealand, while Koloamatangi has also played for Tonga.
"The Australian Kangaroos are steeped deep in heritage. Those guys have a connection with the Kangaroos jersey," Walters said.
"It's great Tino, Kotoni and Keaon have committed.
"I've spoken to all three players, and certainly in Kotoni and Tino's case they have unfinished business in the Australian jersey.
"They have the opportunity to right a few wrongs."
AUSTRALIA SQUAD FOR ASHES
Isaah Yeo (capt), Blayke Brailey, Patrick Carrigan, Nathan Cleary, Xavier Coates, Lindsay Collins, Reuben Cotter, Angus Crichton, Tom Dearden, Dylan Edwards, Tino Fa'asuamaleaui, Harry Grant, Keaon Koloamatangi, Zac Lomax, Mitchell Moses, Cameron Munster, Mark Nawaqanitawase, Jacob Preston, Gehamat Shibasaki, Lindsay Smith, Kotoni Staggs, Ethan Strange, Reece Walsh, Hudson YoungÂ
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