Peavy, who won the Cy Young award in 2007, was shipped by the Chicago White Sox to Boston as the Red Sox prepared for what could be a dog fight for the AL East title with Tampa Bay, Baltimore and possibly the arch-rival New York Yankees.
The trade also involved the Detroit Tigers, who picked up Boston infielder Jose Iglesias. Iglesias, who has been playing third base in Boston, was a potential replacement for Jhonny Peralta, who is in jeopardy of a significant suspension in Major League Baseball's most-recent probe of performance enhancing drugs, MLB.com said.
The Tigers, who lead the NL Central, sent right-handed reliever Brayan Villarreal and outfielder Avisail Garcia to Boston. Garcia was immediately relayed to Chicago.
The Red Sox also sent minor league right-handers J.B. Wendelken and Francelis Montas and minor league infielder Cleuluis Rondon to the White Sox.
Peavy was 8-4 for Chicago this season with a 4.28 ERA in 13 starts. His presence would bolster the Boston staff while Clay Buchholz remains out with a right bursa sac strain.
Garcia sported a .241 batting average for first-place Detroit as of Tuesday with two home runs and 10 RBI. Iglesias was hitting .330 with one home run and 19 RBI.