Terms of the signing announced Wednesday were not released. The Chiefs released defensive lineman Atiyyah Ellison to make room on the roster.
Simoneau hasn't played since he suffered a back injury in 2007. He has 68 starts in 123 career games.
Atlanta made Simoneau was a third-round draft pick in 2000 out of Kansas State, where he had 400 career tackles. He played with Atlanta from 2000-2002, Philadelphia from 2003-2005 and New Orleans in 2006 and 2007.
The Chiefs also said Wednesday they added rookie wide receiver Jeremy Horne to the practice squad.