The Diamondbacks activated Kelly (back) from the 15-day injured list Tuesday.
Kelly is set to make his season debut Tuesday in Baltimore after getting a late start due to a back injury. The veteran right-hander threw six innings and 83 pitches in an extended spring training game last week, so he should be able to handle close to a full workload against the Orioles. Brandon Pfaadt has been demoted to the Diamondbacks' bullpen to accommodate the return of Kelly.