Williams was called up by the Pirates on Tuesday, Travis Sawchik of the Pittsburgh Tribune-Review reports.
A second-round pick by the Marlins in 2013, Williams earned his first major league callup on the strength of a 2.53 ERA and 1.21 WHIP in 20 appearances (19 starts) with Indy this season. He has displayed solid control throughout his minor league career but Williams allows quite a bit of contact (6.5 K/9 in minors), and that may lead to some initial struggles against big league hitters.