The deal will pay Maine about $3 million if he makes the big league club, and includes an "out" clause that allows Maine to become a free agent if he's not added to the major league roster early in the regular season, a baseball source told ESPN.com.
Maine, who has received an invitation to the Rockies' big league camp, is expected to join his new team Saturday in Arizona.
Maine, 29, has a 41-36 record and a 4.35 ERA in seven seasons with the Baltimore Orioles and New York Mets. He went 15-10 with a 3.91 ERA in 191 innings for the Mets in 2007, but has struggled to overcome shoulder problems in recent years. He underwent season-ending surgery in July to clean out scar tissue in his right shoulder.
If Maine is healthy, he will compete for a spot at the back end of the Colorado rotation. The Rockies' rotation currently consists of Ubaldo Jimenez, Jorge De La Rosa, Aaron Cook, Jhoulys Chacin and Jason Hammel.
Senior writer Jerry Crasnick covers Major League Baseball for ESPN.com.