Detroit made the move Thursday before playing the Baltimore Orioles in a spring training game.
Pelfrey was entering the second season of a $16 million, two-year deal. He went 4-10 with a 5.07 ERA last season with the Tigers.
The 33-year-old Pelfrey is 65-91 with a 4.57 ERA in a career that started in 2002 with the New York Mets and included a three-season stint in Minnesota.
He won 38 games from 2008 through 2010 with the Mets and has not won more than seven games in a single season since that stretch.