No financial terms were disclosed. The Seattle Times reported that it was much better than the one signed by last year's No. 11 overall pick, Dwight Freeney of Indianapolis, who got $9.4 million over five years.
The 5-11, 199-pound Trufant is a native of Tacoma, Wash., and was joined at his signing by mother, Constance, and brother, Desmond.
""This is a great day for me and my family," he said. "I'm excited to get over to Cheney and get out on the field with my team and make Seahawks fans proud."
The Seahawks begin training camp Friday in Cheney, Wash.
The Times also reported the signing of safety Ken Hamlin, the team's second-round pick out of Arkansas, to a four-year deal.
No financial terms were released.