At the centre of an eligibility tug of war for most of this year, Tabuai-Fidow was ruled out of end-of-season Tests when he injured his knee in the final round.
The Queensland State of Origin star made his Test debut for Samoa in the 2022 World Cup, before representing Australia for the past two years.
He was likely to play for Samoa this year before injury struck, where Tabuai-Fidow would have joined Payne Haas in switching allegiances from the Kangaroos.
But the 24-year-old confirmed his return to Samoan blue at a fan day on Thursday, drawing cheers from the close to 10,000 people at the team's Brisbane fan day.
"It's absolutely huge, it's been in the pipeline for quite some time," Samoa coach Ben Gardiner told AAP.
"To be able to have the opportunity like this today to make a huge announcement leading into next year's World Cup is pretty exciting for us."
Tabuai-Fidow's call comes with Samoa already fielding six current State of Origin players in Sunday's Pacific Cup blockbuster against Tonga.
Stephen Crichton is also set to return to their backline for next year's World Cup, while Taylan May has also been ruled out of this year's Pacific Cup with injury.
Tino Fa'asuamaleaui is also yet to decide who he will play for at the World Cup, after opting to go on this year's Kangaroos tour with the Australians.
Tabuai-Fidow could likely wear the No.1 jersey in next year's tournament, depending on if Roger Tuivasa-Sheck leaves for rugby.
"It boosts the team, and it inspires the team to know there is another elite player coming to join us," Gardiner said.
"It adds a different dynamic to the team. He adds speed and another real big game breaker for us.
"We're looking at this week and this tournament first. But we're making no secret that we're working our way towards the World Cup in 2026."
The Tabuai-Fidow news came as Samoan officials sought an exemption from the NRL to have hooker Jazz Tevaga play at Suncorp Stadium on Sunday.
Tevaga was one of three players placed in an 11-day concussion stand-down after suffering a head clash in the first half of last weekend's 24-18 loss to New Zealand.
It's understood Samoan officials believe the hooker has not shown any concussion symptoms since leaving the field, and should be cleared to line up against Tonga.
Samoa have called Melbourne second-rower Ativalu Lisati into their squad and onto the bench, with Jaydn Su'A missing Sunday's clash through concussion.
Tyrone May has also joined the squad as cover after playing halfback in Hull KR's Super League grand-final win.
His brother, Terrell, is also some chance of recovering from a hamstring injury in time to face Tonga, after being injured in the lead up to the loss to the Kiwis.Â
In contrast to Samoa's issues, Tonga have been able to name a full-strength squad for the clash, with no surprises after having the first week of the competition off.
Melbourne prop Stefano Utoikamanu and Sydney Roosters centre Robert Toia are two of the notable debutants, with a record crowd for a Pacific Test expected.
Utoikamanu, who has previously represented Samoa, will resume hostilities with Haas after the pair faced off in the NRL grand final.
Toia had a breakout season for the Tricolours, winning the Dally M rookie of the year award and impressing on Queensland debut.
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