The Bears also named Chris Tabor as special teams coordinator and Charles London as running backs coach.
Before posting a 37-16 overall record at OR, which included guiding the Ducks to a Pac-12 championship and an appearance in the national championship game in 2014, Helfrich was Kelly's offensive coordinator.
The trio joins new offensive line coach Harry Hiestand as part of the team's staff under new coach Matt Nagy, who was hired on Monday.
But Helfrich could not sustain the success of his first season and was sacked by OR after a 4-8 2016 season, finishing with a 36-17 record in four seasons at the helm.
OR head coach Mark Helfrich, works the sidelines against Arizona State in an NCAA college football game Saturday, Oct. 29, 2016 in Eugene, Ore. With their fast-paced and prolific spread-option offense, the Ducks went 46-7 during that time. Now, he is expected to aid in the development of Bears quarterback Mitchell Trubisky. 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.
Helfrich led the Ducks-known for their explosive record-setting offense-to a 37-16 record in four seasons as coach from 2013-16, including a 24-12 mark in the Pac-12.
The 39-year-old Nagy spent the past 10 seasons working under Andy Reid in Philadelphia and Kansas City.
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.
He takes over a 5-11 team that missed the playoffs for the seventh straight season and hasn't finished above.500 since Lovie Smith got fired after going 10-6 in 2012.