Fifita, who captained the Australia Prime Minister's XIII earlier this month to a 60-10 victory over their PNG counterparts, joins halfback Sam Walker, hooker Blayke Brailey and centre Bradman Best for Kangaroos debuts in Sunday's World Cup clash against the Bati at Suncorp Stadium.
The 26-year-old Fifita previously played four Tests for Tonga at the 2022 World Cup. His career had stalled at the Gold Coast Titans but his move to the Rabbitohs this year under former Brisbane coach Wayne Bennett led to him finding his best in the NRL this season.
He will start in the back-row alongside North Queensland co-captain Reuben Cotter.
Walker gains his first start in an Australian jersey after a year including a premiership with Sydney Roosters and a stellar State of Origin series debut for Queensland.
The leg injury that ruled Mitchell Moses out of this year's World Cup, sustained in the 24-22 win over New Zealand last week, has opened the door for Walker to make a claim on the No.7 jersey for the rest of the tournament.
Cronulla hooker Brailey and Newcastle centre Best were key figures in NSW's 2-1 series win in this year's Origin series, where they made a name for themselves as big game performers.
Sydney Roosters skipper James Tedesco will play his first match for Australia in three years as starting fullback, with Reece Walsh listed at No.18 on an extended bench. Tedesco will also captain the side with regular skipper Isaah Yeo being rested.
The Kangaroos have revamped their starting pack with Keaon Koloamatangi and Lindsay Smith in the front row and Cameron Murray moving up to No.13 after coming off the bench against the Kiwis.
Tonga can wrap up a semi-final spot with a win over Lebanon on Friday night in Sydney, where Dolphins second-rower Kulikefu Finefeuiaki has his first game of the World Cup. Outside backs Sione Katoa and Paul Alamoti also get their first starts.
Sua Fa'alogo, Samoa's four-try hero from the 78-4 win over France, moves from the bench to start on the wing against Papua New Guinea in Port Moresby on Saturday with winger Deine Mariner (hamstring) out of the 19.
England have stuck with the same 19 that lost 30-12 to Tonga for their match against France in Perth, also on Saturday. The Brian McDermott-coached side needs a huge win to keep their remote semi-finals hopes alive.
Gold Coast pocket rocket Keano Kini starts in place of the injured Kalyn Ponga at fullback for the Kiwis' must-win showdown with Cook Islands in Christchurch on Sunday.
Warriors forwards Tanner Stowers-Smith and Jacob Laban make their Test debuts for New Zealand off the bench.
The Aitu welcome back star fullback Valentine Holmes, who missed the loss to Fiji with an ankle injury.
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