Marquez will start Wednesday against the Cardinals, Thomas Harding of MLB.com reports.
The 21-year-old will step in for his first career start at the major league level, with Jeff Hoffman presumably demoted to the bullpen for the time being. Through three appearances with Colorado, Marquez has more walks (4) than strikeouts (3), but he posted a 155:39 K:BB between Double-A and Triple-A this year. The right-hander managed at least five strikeouts in all five starts for Triple-A Albuquerque, but he also gave up five home runs in those five starts.