Nanai has been in a two-way tug-of-war between Queensland and New Zealand in recent months.
The 19-year-old second-rower was born in New Zealand but moved to Cairns just before his 13th birthday to make him eligible, playing most of his junior football for the Cairns Kangaroos before joining the Cowboys' pathway.
Making his debut at the end of last season for the Cowboys, he has become a permanent member in Todd Payten's side early in 2022, recently re-signing for 2023 as well at the club.
The teenager played all six games so far this year, crossing for five tries and running for 97 metres per game on the edge.
While defensive weaknesses still exist in his game, Queensland have pulled off a major coup by having him commit, with Nanai telling News Corp that he has made up his mind, wanting to follow in the path of club great Johnathan Thurston.
It's understood Michael Maguire had offered Nanai a spot in the Kiwis squad for the end-of-year World Cup, such was the desire of the NZRL to get him on board.
“I have made my decision. I want to play for the Maroons, 100 per cent,” Nanai said.
“I would love to run onto Suncorp Stadium and give it to the Blues fellas.”
Nanai would be considered a bolter for this year's Queensland team under new coach Billy Slater, with Kurt Capewell, David Fifita, Jaydn Su'A, Felise Kaufusi and Jai Arrow in contention for the back row spots alongside the young gun.