The Diamondbacks selected Scott's contract from Triple-A Reno on Tuesday.
Scott will come up alongside Kevin Ginkel and Bryce Jarvis to replace Jeff Brigham, Justin Martinez (elbow) and Christian Montes De Oca (elbow) in Arizona's bullpen. Scott, 33, turned in a 5.40 ERA and 1.68 WHIP in 16.2 innings during his time with the Astros this year, though he's fired 3.1 shutout innings in Triple-A since joining the D-backs organization.