The team announced the deal Wednesday.
Crombeen would have been a restricted free agent on July 1. The 25-year-old has spent the past three seasons with the Blues, including a career high 80 games last season. He registered seven goals and 14 points. Crombeen has 26 goals and 53 points in 248 career games over four seasons.
Crombeen was drafted by the Dallas Stars in the second round (54th overall) of the 2003 NHL draft. The Blues claimed him off waivers in 2008.