With Clay Buchholz on the disabled list with a shoulder problem, the move gives Boston another proven starter for the stretch run in the tough AL East. It also could strengthen the bullpen if the Red Sox decide to return rookie Brandon Workman to a relief role if Buchholz comes back.
"We thought Peavy, of the starting pitchers available, was the right fit for us," Cherington said. "It just came together that this was the deal we thought made the most sense."
The Red Sox also got reliever Brayan Villarreal from the Tigers. They shipped Iglesias to Detroit and three minor leaguers to the White Sox as part of the trade.
Chicago also received prized prospect Avisail Garcia. Garcia, who turned 22 in June, hit .374 with five homers and 23 RBIs in 33 games for Triple-A Toledo.
The outfielder, who was the Tigers' minor league player of the year last season, was assigned to Triple-A Charlotte.
"We're very excited about his upside," general manager Rick Hahn said. "We truly feel this is a five-tool player, someone who's not only going to hit for average but for power, run well, play above-average defense.
"He's still young and he still has a little bit of development ahead of him, but we feel we've acquired someone with a great deal of upside who's going to have a big impact on the South Side for many years to come."
Peralta is among a group of players who have been linked in media reports to Biogenesis, a closed Florida anti-aging clinic that was accused by Miami New Times in January of distributing banned performing-enhancing drugs, sparking an investigation by Major League Baseball. The league could hand down multiple suspensions as part of the case in a matter of days.