Howard, 37, most recently spent time in the Atlanta Braves organization before he was released from his minor league contract on May 8.
A three-time All-Star and former National League MVP, Howard once ranked among the game's premier power hitters during a prime that stretched from 2006-2011.
Over the course of that six-year window, Howard clobbered 262 home runs and drove in a whopping 796 runs.
However, Howard's run as a franchise centerpiece came to an end in October 2011 when he suffered a torn Achilles tendon in the postseason against the St. Louis Cardinals.
After that debilitating injury, Howard was never able to return to form and batted better than .230 just once (2013) during his final five years in the City of Brotherly Love. Howard was also plagued by a lack of discipline at the plate and struck out 636 times between 2012-2016.
The Rockies can't expect much out of Howard since he's pushing 40, but he is a worthwhile flier who could pay dividends come playoff time as a pinch hitter if he proves capable of harnessing bits and pieces of his prime form.