The deal was reported Monday but couldn't be completed until the new NFL year became Tuesday.
Despite being limited to nine games last season, Harvin caught 62 passes for 677 yards. He was leading the NFL in kick return average (35.9 yards) before an ankle injury in a Week 9 game against Seattle.
The Vikings will have Seattle's first-round pick and a seventh-round choice this year along with a third-round pick in 2014 in exchange for Harvin, who reportedly was having issues with Vikings management.
Over a four-year NFL career, Harvin has 280 catches for 3,302 yard and 20 touchdowns. He's also returned five kickoffs for touchdowns.