Rockies manager Bud Black announced Tuesday that Trejo made the Opening Day roster, Thomas Harding of MLB.com reports.
The 27-year-old was in camp as a non-roster invitee after being outrighted off the 40-man roster in January, but he'll be added back to the major-league roster ahead of Thursday's season opener in Arizona. Trejo appeared in 83 games for Colorado last season and had a .232/.288/.343 slash line.