Thornton (elbow) was activated from the 10-day injured list Thursday.
Thornton will start Game 2 of Thursday's doubleheader against the Phillies, so the transaction was anticipated. He was placed on the IL earlier in August while dealing with right elbow inflammation but progressed smoothly through his recovery. The right-hander should claim a role in the starting rotation with Nate Pearson (elbow) on the 10-day injured list.