Runzler's contract was purchased from Triple-A Indianapolis on Sunday.
Runzler had a solid season with Indianapolis, as he built a 3.05 ERA and 1.57 WHIP over 40 games (41.1 innings). The 32-year-old has some MLB experience but last appeared in the show in 2012 while on the Giants. He'll likely be used by Pittsburgh in low-leverage situations.