Andersen will start on Jan. 9, when the NCAA is allowing coaching staffs to expand to a 10th assistant.
Andersen has been a head coach at three FBS schools -- Utah State (2009-12), Wisconsin (2013-14) and Oregon State (2015-17) -- since last being with the Utes. He has a 52-54 record as an FBS head coach, and was 1-5 with the Beavers before stepping away in October and leaving behind about $12.6 million in guaranteed money.
Andersen's first stint at Utah was as a defensive line coach under head coach Ron McBride from 1997 to 2002. He spent a year as head coach at Southern Utah before returning to Salt Lake City and working for Urban Meyer for a season and then as defensive coordinator for Kyle Whittingham from 2005 to 2008.
"We're looking forward to Gary rejoining our staff," Whittingham said in a statement.
"Gary brings a wealth of high-level coaching experience to the program, including serving as the head coach at two Power Five schools. During his previous time on our staff, he developed some of the best defensive linemen in Utah history."
Andersen was a center at Utah in 1986 and 1986 after playing in junior college.