The six-time Queensland representative will be 31 by the time his new deal expires at the end of the 2027 season.
Initially a second-rower, Hess has found success on a shift to the middle of the park in recent years, though is sidelined for the entire 2024 season with an anterior cruciate ligament injury suffered in the pre-season challenge.
"(Hess) has been a huge contributor to this club over a long period of time and is a point of difference for us on the field with the work he churns through as well as his enthusiasm and intensity," Cowboys football boss Micheal Luck said.
"We're excited to have another North Queensland junior taking another step towards becoming a one-club player."
A handful of the Cowboys' NRL regulars remain without contracts beyond this season, with the club needing to make a call on the future of premiership-winning veterans Kyle Feldt, Jake Granville and Chad Townsend.
Co-captain Reuben Cotter, highly paid Queensland centre Val Holmes and NSW hooker Reece Robson are off-contract at the end of next year and can field rival offers from November.
Hess made his NRL debut late in the Cowboys' 2015 premiership season but did not appear on grand-final day, only firming as a regular first-grader in 2017.
That year, he started from the bench in the grand-final loss to Melbourne, the Cowboys' most recent appearance in the decider.
The 27-year-old received the Paul Bowman Medal as North Queensland's player of the year in 2021 and has made 165 appearances for the club in total.
Hess's previous deal was until the end of 2024 and could have negotiated with NRL rivals since last November.
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