Helfrich, 44, spent his year out of coaching as a college football analyst for Fox Sports.
Helfrich is Nagy's fourth reported coaching hire and the first without ties to Lovie Smith's Bears staff.
Mark Helfrich: The former OR head coach will serve as Nagy's offensive coordinator, although Nagy is expected to call his own plays.
He then worked as quarterbacks coach at Boise State (1998-2000) and Arizona State (2001-05) before serving as offensive coordinator and quarterbacks coach at Colorado (2006-08).
Helfrich becomes the second coordinator to be hired after the Bears named Chris Tabor as special teams coordinator on Wednesday.
The Browns ranked sixth in kickoff return average against (21.8), seventh in the National Football League in punt return average (9.9), ninth in total kick return yards (8,974) and 10th in total return yards allowed (7,627) since Tabor joined Cleveland in 2011. His career, which began at Southern Oregon University, his alma mater, in 1996 as a running backs coach, has been spent exclusively at the college level to this point.
It also signals the Bears' need to add speed and dynamic playmakers after the catch to an offense that was severely lacking in both areas, except for rookie sensation Tarik Cohen, whose upside is exciting with the new creative offensive minds on board. This past season the Texans, finished seventh in the AFC with 115.1 rushing yards per game. Still, the Bears and Nagy were eager to retain Fangio; their highly respected and veteran defensive coordinator who inherited one of the NFL's worst defenses in 2015 and coached the unit back to respectability over the last three seasons. They have resided in last in the NFC North four straight seasons.