Bard, a 28-year-old right-handed reliever and onetime starter, was a dominant late-inning pitcher from 2009-11, but issues with his confidence and injuries derailed his career in Boston. He pitched in only two games for the Red Sox this season before he was sent to the minors.
"This guy was arguably one of the best set-up guys in baseball just a few years ago. Now he's healthy," Cubs manager Dale Sveum said Wednesday. "Theo [Epstein, Cubs president of baseball operations] has a lot of confidence in him. He was one of the best, if not the best, not too long ago."
Selected by the Red Sox in the first round (28th overall) of the 2006 draft, Bard struggled in three minor league stops after being sent down this season, pitching just 6 1/3 innings with 10 wild pitches and 23 walks between Double-A Portland, the Gulf Coast League and short-season Lowell.
Bard set Red Sox team records for holds in both 2010 and '11 with 32 and 34, respectively. His 79 career holds from 2009-11 were the most ever by a major leaguer in his first 192 appearances.
The Red Sox made Bard a starter before the 2012 season, but he struggled, going 4-6 with a 5.30 ERA in 10 starts.
The move reunites Bard with Epstein, the former Red Sox general manager who drafted him.
"Not surprised that the Cubs would claim him, given the familiarity with Theo and Jed [Hoyer, current Cubs GM and former Red Sox assistant GM], who drafted him here," Red Sox manager John Farrell said. "And I guess the most important thing is we wish him well and hope he gets back on track. There's still a good pitcher in there once he gets back on track."
Farrell still believes the right-hander can be effective.
"I'm not going to say that he can't," Farrell said. "There's still a player and a pitcher there that's motivated. And yet any time there's activity disrupted by an injury, it's going to slow that process. Time was of the essence to us; we needed a roster spot. Based on what we saw the last couple of years, it needs to be built back gradually, and however long that takes is the unknown in this."
To make room for Bard on the 40-man roster, the Cubs designated outfielder Cole Gillespie for assignment.
Also on Wednesday, the Cubs selected the contract of reliever Chang-Yong Lim from Triple-A Iowa, while designating pitcher Michael Bowden, another former Red Sox, for assignment.
Information from ESPNChicago.com's Jess Rogers and ESPNBoston.com's Joe McDonald was used in this report.