The source said the deal will officially be announced Friday. Corpas took a physical in Chicago on Thursday. The finances of the deal are not yet known.
Corpas was an integral part of the Colorado Rockies team that went to the World Series in 2007. That season, Corpas had a 2.08 ERA and 19 saves in 78 appearances for the Rockies.
The right-hander had Tommy John surgery in 2010. He was signed to a minor league deal by the Texas Rangers during the 2011 season, but didn't pitch in an organized game. He threw some innings in September in instructional ball and pitched in Panama over the winter.
The Cubs are expected to make official Sean Marshall's trade to the Cincinnati Reds in the coming days. Adding Corpas will help fortify the team's bullpen. Furthermore, this move could be a precursor to the Cubs giving Jeff Samardzija a chance to make the rotation in 2012.
Corpas has a 12-16 record and 3.93 ERA in 280 career appearances.
Bruce Levine covers the Cubs for ESPNChicago.com.