Farrell had his contract selected from Triple-A Iowa and will start for the Cubs against the Cardinals on Wednesday, Meghan Montemurro of the Chicago Tribune reports.
Farrell joined Chicago on a minor-league deal in April and has a 5.03 ERA, 1.46 WHIP and 49:28 K:BB across 59 innings at Triple-A this year. It's likely to be a spot start for the 31-year-old, who has a 4.93 ERA over 63 career appearances in the big leagues.