Holliday reported to the rookie-level Grand Junction Rockies on Sunday.
The 38-year-old Holliday played in Colorado from 2004 to 2008, achieving his greatest success with the team. He led the National League in batting average and RBIs in 2007, when the Rockies got all the way to the World Series. He hit .340 with 36 home runs and 137 RBIs that season, all career highs.
Holliday was traded to the Oakland Athletics in 2009 after he and the Rockies could not come to an agreement on a contract extension. He signed with the Cardinals in the offseason and was part of a St. Louis team that won the World Series in 2011.
A seven-time All-Star, Holliday has a .299 average with 314 home runs and 1,217 RBIs over 14 seasons.
Last season, he played with the New York Yankees, hitting .231 with 19 homers and 64 RBIs.
Colorado is 56-47, two games back of the Los Angeles Dodgers in the NL West and in a fight for a wild-card spot.
The Associated Press contributed to this report.