Lopez, 32, spent the past four seasons with the Boston Red Sox organization. In that span, he pitched in 172 games for the Red Sox with a 3.30 ERA.
The Pirates on Friday filled three coaching vacancies in their minor league system.
The new Class A franchise in Bradenton, Fla., will be named the Marauders.
Zach Duke, Paul Maholm and Ross Ohlendorf are locks for the starting rotation. It would require some sort of near-catastrophic event for Charlie Morton to be out of the No. 4 spot.
The Pirates are ready to sign shortstop Bobby Crosby to a one-year contract.