The move Tuesday came two days after he helped the Red Sox sweep Colorado in four games to win their second World Series title in four years.
During the regular season, Schilling said he doubted he would be re-signed, but said on his radio show he would seek a one-year deal in Boston or elsewhere.
The 40-year-old right-hander is among the nearly 100 players filing for free agency this week, 43 on Tuesday.
"I would love to be able to come back and pitch one last season and win a World Series and walk away," he said on the team's Web site.
"A one-year deal is all I'm looking for."
The highlight of his 2007 season was a one-hitter at Oakland June 8.
The free agency list includes Red Sox pitcher Matt Clement and outfielders Eric Hinske and Bobby Kielty, along with other well-known players like Alex Rodriguez, Barry Bonds, Mike Piazza, Kenny Lofton and Torii Hunter.