Jackson, who will enter his sixth NFL season, has spent his career with the Minnesota Vikings, where he has served as Brett Favre's backup the past two seasons. Jackson has made 20 career starts, with his most significant playing time coming in 2007 when he started 12 games, throwing for 1,911 yards, nine touchdowns and 12 interceptions.
With the Seahawks expected to be without Matt Hasselbeck this season, Jackson figures to compete with Charlie Whitehurst for Seattle's starting job. The Seahawks also are expected to sign Matt Leinart -- who played for coach Pete Carroll in college at Southern California -- according to NFL Network insider Jason La Canfora. La Canfora also reports that, with the signing of Jackson, the Seahawks are effectively out of the trade sweepstakes for Eagles quarterback Kevin Kolb, adding that the team had reservations about how steep the price would be in trade and financial compensation.
Reports surfaced Tuesday afternoon that the Seahawks told Hasselbeck he was no longer in their future plans. Hasselbeck and his agent did not return messages left by The Associated Press.
The decision to move on from Hasselbeck contradicted Seattle coach Pete Carroll's pronouncement in January that re-signing Hasselbeck was Seattle's No. 1 priority. The two sides could not reach an agreement before the NFL lockout.
Hasselbeck spent the past 10 seasons in Seattle and for much of that time was the face of the franchise. Whitehurst was supposed to challenge Hasselbeck for the job before the 2010 season, but his only two starts last season came in games Hasselbeck was injured.
Hasselbeck seemed to affirm his importance to the franchise by leading Seattle to a stunning NFC first-round playoff upset of New Orleans before the Seahawks lost to Chicago in the NFC divisional playoff.
"You're more experienced; it goes for all of us. There were a bunch of new guys this past season," Whitehurst said. "I think everybody is probably feeling pretty confident about this season."
Instead of Whitehurst battling Hasselbeck for the starting job, he'll be competing with Jackson. Later in the day, after learning the reports of Hasselbeck's departure, Whitehurst seemed to realize his chance.
"It's as good an opportunity as I'm going to get, and I'm looking forward to it," he said.
In Minneapolis, Jackson was ushered aside most of the last two seasons in favor of Brett Favre. Now he'll get a fresh start in Seattle and be reunited with offensive coordinator Darrell Bevell, who is in charge of revamping Seattle's passing game. Bevell spent the previous five seasons as Minnesota's offensive coordinator.
Hasselbeck had been instrumental in organizing offseason workouts for players in the Seattle area and working with the University of Washington on using their facilities. Some players had been extremely outspoken on Twitter in urging the Seahawks to re-sign the veteran QB.
NFL Network insider Michael Lombardi, NFL Network insider Jason La Canfora and The Associated Press contributed to this story.