Garza has been out since early in spring training with a lat injury after missing most of the second half of last season with an elbow problem. He last pitched in a major league game on July 21, 2012.
"I'm excited and happy I don't have to rehab again," Garza said Saturday. "This actually means something, so I can't wait. It's been 10 months in the making, I'm excited to get back out there."
Garza threw 75 pitches in six shutout innings at Triple-A Iowa on Thursday. Cubs manager Dale Sveum said Garza would likely be held to around 85 to 90 pitches against the Pirates.
"You can never have enough quality starting pitching, so you always want an arm like Garza's in your starting rotation," Sveum said.
To make room for Garza in the rotation, Carlos Villanueva has been moved to the bullpen.
To clear a roster spot for Garza, the Cubs designated for assignment reliever Michael Bowden, who was 1-2 with a 3.78 ERA in 14 games this season. They also claimed right-handed pitcher Eduardo Sanchez off waivers from the St. Louis Cardinals.
"It's a way to get another power arm that we really don't have in the minor leagues," Sveum said of the Sanchez pickup. "We're trying to get some power arms in this organization."
Sanchez, 24, is 3-2 with five saves in his career but hasn't appeared in a major league game this season. He had a 3.72 ERA with one save in nine games with Triple-A Memphis this year.
Sanchez will report to Triple-A Iowa.