Janikowski, 41, told ESPN on Sunday that his body couldn't handle another season in the league.
"It was a good run," Janikowski said. "I still think of the Super Bowl -- it still hurts."
Janikowski and the Raiders lost 48-21 to the Tampa Bay Buccaneers in Super Bowl XXXVII during the 2002-03 season.
The Raiders originally selected Janikowski in the first round (No. 17 overall) in the 2000 NFL Draft. The kicker's retirement leaves New England Patriots quarterback Tom Brady as the last remaining active player from the 2000 draft class.
Janikowski earned more money in his professional career than any other kicker in league history. He made $53.29 million during his time in the NFL, according to Spotrac.
The Raiders let Janikowski enter free agency after 18 seasons and he signed a one-year deal with the Seahawks on April 13, 2018. He was 22-of-27 on field-goal attempts last season.
Janikowski's 1,913 career points are 10th in NFL history. His 436 made field goals are tied for ninth with former Denver Broncos and Atlanta Falcons kicker Jason Elam. He has a league-record 58 field goals of 50 yards or more, including a 63-yard kick against the Broncos in 2011.