No terms were disclosed, but the Seattle Times reported the deal is worth $50.2 million, including a $10 million signing bonus, with $28 million to be paid out over the first three years.
The 27-year-old Trufant has developed into one of the NFL's top shutdown cornerbacks since he was a first-round draft pick (11th overall) by the Seahawks in 2003 out of Washington State.
"You know what's right and you know where you're supposed to be at the end of the day," he said. "It just felt like I'm always supposed to be a Seahawk."
The 5-foot-11, 197-pounder made his first Pro Bowl appearance last season after making seven interceptions and 85 tackles (78 solo) in the regular season.
He is the latest young Seattle player to sign a long-term deal during the offseason.
The other was Pro Bowl linebacker Lofa Tatupu.