Hart would have become a free agent at the conclusion of the World Series anyway, so the move merely speeds up the process for the 10-year Major League veteran, who struggled in his lone season with the Mariners on a one-year deal signed as a free agent last winter.
Hart, 32, hit .203 with six home runs and 21 RBIs in 68 games after signing a $6 million deal. The two-time National League All-Star spent a good part of the season on the disabled list with a hamstring strain and then knee issues after missing all of 2013 with the Brewers following microfracture surgeries to both knees.
Seattle's other free agents will be pitchers Joe Beimel and Chris Young, outfielders Endy Chavez and Chris Denorfia, catcher Humberto Quintero and designated hitter Kendrys Morales. Outfielder Franklin Gutierrez also becomes a free agent after spending the year on Seattle's restricted list following his decision to not report to camp last February.
Those players will be free to sign with any MLB team at the conclusion of the World Series.
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. This story was not subject to the approval of Major League Baseball or its clubs.