Volquez, 30, went 9-12 with a 5.71 ERA (60 ERA+) and a 1.84 K/BB in 170 1/3 innings for the Padres and Dodgers this past season. San Diego released him in August after he went 9-10 with a 6.01 ERA (57 ERA+) in 27 starts.
Volquez has been inconsistent and occasionally brilliant throughout his career, but the Pirates signed a similar pitcher in Francisco Liriano last offseason, and he became a Cy Young contender. They're hoping to pull off the same kind of turn-around with Volquez.
The signing seems to make it unlikely that A.J. Burnett will return to Pittsburgh next season. He's been debating whether to continue pitching or retire. Volquez will join Charlie Morton, Gerrit Cole, Jeff Locke, Wandy Rodriguez and Liriano as rotation candidates.