Nanai, 19, exploded on the scene in 2022, earning representative honours for Queensland in all three State of Origin games and for Australia in the World Cup-winning squad.
He took out the Dally M Rookie of the Year in 2022 after scoring 17 tries - the most in a single season by a forward in club history.
Nanai is a north Queensland junior, coming through the Cowboys' Cairns Academy before joining the NRL squad straight out of high school ahead of the 2021 season.
With rival clubs swooping for his signature and mega-deals offered, Nanai signed a one-year deal last season before committing his long-term future to the Cowboys on Wednesday.
"I've always wanted to stay here - this is my home - and I'm glad my manager got it done," Nanai told reporters.
"I wanted to get it done before the season started and a lot of pressure off my chest. Now I can focus on footy and hopefully have a great year again."
Cowboys general manager of football Micheal Luck said Nanai was integral to success in the club's future.
He is the final piece of a young core group to commit to the club long-term after many of their emerging stars signed extensions in 2022.
Five-eighth Tom Dearden is signed through 2024, hooker Reece Robson, Griffin Neame and Heilum Luki through 2025 and outside backs Murray Taulagi and Scott Drinkwater are on the books through 2027.
"Signing Jeremiah to a long-term extension is fantastic news for our club," Luck said.
"He can do things in games very few other players have the ability to do. He is a point of difference for us with the ball and defensively he reads play exceptionally for someone of his age and experience level.
"Aside from securing one of the best young talents in the NRL, we now have the key pieces of our team across the park under contract for multiple seasons."
