To make room for Turner on the 40-man roster, the Cubs designed outfielder Ryan Kalish for assignment.
Turner, 23, was selected by the Detroit Tigers in the first round (No. 9 overall) of the 2009 draft and traded to the Marlins in 2012 as part of the deal that sent Anibal Sanchez to the Tigers.
Turner split time this season between the Marlins rotation and bullpen, going 4-7 with a 5.97 ERA. He is 9-21 with a 4.77 ERA in 53 major league appearances (45 starts) over the past four seasons with the Marlins and Tigers.
''He was one of the better starting pitching prospects in all of baseball a couple of years ago and we feel like that talent is still in there,'' Cubs president Theo Epstein said. ''If you look at his velocity, it's still there. If you look at some of the peripheral numbers, they're still pretty decent.
''We've had some success with talented pitchers who are going through tough periods, kind of just getting them here and letting them reset a little bit.''