Harden was placed on the disabled list on April 10, retroactive to April 3, with a strained right shoulder, his sixth trip to the DL over the last four years.
Harden took the roster spot of outfielder Chris Denorfia, who was placed on the 15-day DL -- retroactive to Wednesday -- because of tightness in his lower back.
Harden is 1-0 with a 0.82 ERA in two starts this season. He was 1-0 with a 0.93 ERA in two minor league rehab starts.
Over the last four years, Harden has appeared in only 40 games due to injuries, compiling a 16-7 record and 2.81 ERA.
Manager Bob Geren said Harden wouldn't throw more than 90 pitches in his first game back.
"He's medically cleared, he's had the rehab stints," Geren said. "But I don't see him going over 90."
Denorfia has a .260 average with no homers and six RBIs in 25 games this season.