Winger Antonio Winterstein and full-back Lachlan Coote agreed new deals with the Cowboys last month and centre Linnett has followed suit.
The 27-year-old revealed he had no hesitation in committing his future to Paul Green's side, who are in the hunt to retain their NRL crown.
He said: "I always wanted to stay here. When I came up from the [Sydney] Roosters at the start of 2012, I haven't looked back and have thoroughly enjoyed playing with such great team-mates and in such a settled environment.
"This is a fantastic club to play for, and the recent success we've had adds to that enjoyment.
"I've also settled well into the North Queensland lifestyle, having made some great friends away from footy as well."
Linnett has scored 46 tries in 111 appearances for the Townsville club.