Bedard, 33, was 7-14 with a 5.01 ERA in 24 starts for the Pirates this season. The 14 losses tied for the most in the major leagues.
"We were trying to find a rhythm and a rhyme to get him on a roll and weren't able to do it," manager Clint Hurdle said Tuesday. "The decision was made we'd be better served going in a different direction."
The move caught many by surprise in the Pirates clubhouse, where Bedard was well-liked for his quiet but sharp sense of humor and his ability to teach some of the younger players.
The Pirates signed Bedard to a one-year, $4.5 million deal during the Winter Meetings in hopes they could keep the left-handed starter healthy enough to contribute. It was an important season for Bedard -- a chance to convince teams he deserved a multiyear deal.
Bedard stayed healthy and pitched well early, posting a 3.12 ERA in 10 starts over the first two months. But he struggled with consistent command from that point on, and his performance took a drastic, downward turn.
From the beginning of June until his final start Sunday, Bedard went 4-10 with a 6.35 ERA.
His inability to pitch deep into games also put a strain on the rest of the pitching staff, Hurdle said. Bedard failed to pitch past the fifth inning in 14 of his starts.
Bedard met with Hurdle and Pirates general manager Neal Huntington late Monday, and they informed him of the decision.
"He was very professional going out the door," Hurdle said.
Hurdle said the Pirates are still working to determine who will replace Bedard in the rotation and for his scheduled turn Saturday. But the Pirates likely will use a four-man rotation since they have an off day Thursday. They would not need to add a fifth starter until the Houston Astros come to PNC Park next week.
Kevin Correia, who started most of the season until recently moving to the bullpen, is under consideration for that spot, Hurdle said, as are minor leaguers Jeff Locke and Kyle McPherson.
Bedard's release and the uncertainty of Neil Walker's health after experiencing tightness in his lower back Monday prompted the Pirates to recall infielder Chase d'Arnaud from Class AAA Indianapolis Tuesday afternoon. Walker did not start for a second consecutive game after feeling discomfort in his lower back.
He was sent home during the game Monday and arrived late to the clubhouse Tuesday after seeing doctors.
"He felt a little bit better but went to see another doctor," Hurdle said.
D'Arnaud was hitting .247 with six home runs for Indianapolis this season, struggling for much of it after having a concussion in April. He missed more than a month after being hit by a pitch and struggled in his return, hitting .213 before the International League All-Star break.
"I had never really gone through anything like that. I couldn't run, exercise or anything for a month and a half," d'Arnaud said. "I had to go through a whole new spring training in the middle of the season."
D'Arnaud, who primarily played shortstop, has been more successful since the break, hitting .286. In his past 10 games, he is hitting .381 with three home runs, two doubles and five RBIs. He also has played second and third. And he could be valuable as a pinch-runner as he was second in the International League with 33 steals in 97 games this season.
D'Arnaud spent some of the 2011 season with the Pirates, but he was one of the first players sent down in spring training. He hit .217 in 48 games with the Pirates last year.