Seattle sent Bedard and right-handed Minor League reliever Josh Fields to Boston. In return, the Mariners received Triple-A outfielder Trayvon Robinson from the Dodgers and Double-A outfielder Chih-Hsien Chiang from the Red Sox.
The Red Sox, who initially acquired Robinson to make the deal happen, sent Minor League catcher Tim Federowicz, righty Juan Rodriguez and right-hander Stephen Fife to the Dodgers.
General manager Jack Zduriencik said the deal makes the Mariners better in the long run, though he acknowledged it could be tough for Seattle's rotation the last two months of the season now that Bedard and right-hander Doug Fister have been dealt away in the past two days.
"In the big picture, we got two offensive guys that our scouts like a lot," Zduriencik said. "And we make the sacrifice right now to give up two months of Erik Bedard for two more players who will be with us for a long period of time. That's the balance.
"Could we suffer from now to the end of the year? I hope our fans understand there are sacrifices to be made, and it's possible our pitching staff won't be as good with the two guys we just moved. But to get six players in return ... it's about today, but it's also about where we're headed. It's about accumulating talent. That's where we're at."
Bedard, 32, was 4-7 with a 3.65 ERA for Seattle, but missed the past month with a sprained left knee before returning for one start on Friday that lasted just 1 1/3 innings.
Fields, 25, was a 2008 first-round Draft choice of the Mariners who has split this season between Double-A Jackson and Triple-A Tacoma.
Robinson, 23, is a switch-hitter batting .293 with 26 homers and 76 RBIs for Albuquerque in the Pacific Coast League. Chiang, 23, is a left-hander who leads the Eastern League in batting average (.340), RBIs (76), doubles (37), runs (68), slugging percentage (.648) and extra-base hits (59).
"Both players are having very nice years," Zduriencik said. "There's no question we're looking for bats."
Robinson is on the Mariners' 40-man roster and will report initially to Triple-A Tacoma. Chiang will join the Mariners' Double-A team in Jackson.
Zduriencik said the deal came right down to the 1 p.m. PT non-waiver Trade Deadline, with Robinson's inclusion not being raised until the last few hours.
He also said that Boston assumed the remainder of Bedard's one-year contract, which is for a $1 million base, and the two teams had an arrangement in place on how to split his remaining incentives.
Bedard has earned $1.45 million in incentives so far from the Mariners, including $350,000 for making his 16th start of the season on Friday to reach that escalator clause. With two months remaining, he could accumulate another $2.65 million in incentives if he makes 11 more starts and pitches 58 2/3 more innings.
Bedard has been with the Mariners the past four years, going 15-14 with a 3.31 ERA in 46 starts while missing all of 2010 and parts of '08 and '09 with shoulder problems. His shoulder was finally healthy this year after three surgeries, and he pitched very well until spraining his knee on June 27.
He came off the disabled list on Friday, but gave up three hits, four walks and five runs in just 1 1/3 innings in an 8-0 loss to the Rays as he struggled with his location.
"Erik is sad to leave us, but has a degree of excitement in going to a club that has the possibility of being in the playoffs and participating in the World Series," Zduriencik said.
The deal was completed just as the Mariners were taking the field for their 1:10 p.m. PT finale with the Rays, so Bedard was not available for comment.
Zduriencik said the deal "does put a little wrinkle" in the Mariners' pitching rotation for the remainder of the season. Rookie Blake Beavan will start in place of Fister on Monday, but the club will now need someone to step in for Bedard's next scheduled start Wednesday against Oakland.
Charlie Furbush, acquired from Detroit in the Fister trade, is a rotation candidate, but Zduriencik and manager Eric Wedge both said he'd likely need time to be stretched out after pitching primarily out of the bullpen this season.