Flaherty was called up ahead of his start against the Giants on Friday, MLB.com's Jenifer Langosch reports.
Flaherty will make his major-league debut in San Francisco in the wake of Mike Leake's departure to the Mariners. The 21-year-old has made 15 starts at the Triple-A level this season with Memphis, compiling a 2.74 ERA and an 85:24 K:BB in 85.1 innings. Moving forward, Flaherty could wind up getting another opportunity to start depending on the health of Adam Wainwright's elbow, and how he performs against the Giants.