Flacco, 26, played mainly at Single-A Frederick last year, hitting .218 in 103 games. He also played four games at Double-A Bowie and was expected to compete there for the starting first base job along with Aaron Baker and Tyler Townsend.
Flacco was drafted in the 31st round of the 2009 amateur draft out of CCBC-Catonsville.
“Mike had a few years with us and the Red Sox had some interest,” Orioles executive vice president Dan Duquette said. “And we thought this would be a better opportunity for him. We talk to clubs every day to see if we have a match, and on this one we had a match”