Winston, a 30-year-old right tackle, signed a one-year contract, a source told ESPN NFL Insider Adam Schefter, confirming multiple reports.
Winston tweeted out the news that he was joining the defending Super Bowl champions on Tuesday morning.
Season finally starts for me today! Looking forward to chasing a ring with the Seahawks!! Time go to work!- Eric Winston (@ericwinston) July 29, 2014
Winston played for the Arizona Cardinals last season. He was elected the NFLPA president earlier this year.
He said last week he didn't need to be promised a starting job but wanted the opportunity to compete for one. That's what Arizona offered last year, he said, and it worked out in his favor as Winston started all 16 games.
Winston, an eight-year veteran, has spent his offseason preparing for the right call by staying in shape. He worked out this summer with Texans receiver Andre Johnson and running back Arian Foster and former Texan Owen Daniels.
Breno Giacomini, who started at right tackle for the Seahawks last season, signed a free-agent deal with the Jets this offseason. Before Winston's addition, second-year offensive lineman Michael Bowie and rookie Justin Britt had been competing this offseason to fill the right tackle spot.
Winston played his first six NFL seasons with the Texans, joined the Chiefs in 2012 and the Cardinals last season. Winston has started 119 consecutive games, the second-longest streak for an active player. He also has played in 124 straight regular-season games, also second-most among active players.
ESPN.com Cardinals reporter Josh Weinfuss contributed to this report.