Milone was confirmed by manager Scott Servais as the starter for Tuesday's game against the Rangers, Ryan Divish of The Seattle Times reports.
Milone was with the team in Texas on Monday, so the announcement is no surprise. The 32-year-old journeyman has a 4.62 FIP and 43:12 K:BB in 49.1 innings at Triple-A. A corresponding move to clear a roster spot should come Tuesday once he's officially promoted.