A corresponding roster move will be made before Tuesday's game against the Cardinals, the club announced.
Bedard, 33, signed with the Pirates as a free agent this past offseason and made 24 starts. He went 7-14 with a 5.01 ERA in 125 2/3 innings.
He has not gone more than five innings in four of his last five starts, allowing a combined total of 22 runs in 25 2/3 innings of work in that span.
Bedard has pitched for the Orioles, Mariners, Red Sox and Pirates in his nine-year career.
Opening a key three-game series against the National League Central-rival Cardinals on Monday night, Pittsburgh took its sixth loss in seven games to fall three games behind second-place St. Louis in the division. In the NL Wild Card race, the Bucs are a half-game behind the Dodgers, who are 2 1/2 games behind the second spot, currently held by the Cards.