DeRuyter, 54, was fired in October after Fresno State started his fifth season at 1-7. He went 30-30 at the school.
He previously served as defensive coordinator at Texas A&M, where he coached standout linebacker Von Miller. DeRuyter has also been defensive coordinator at Air Force, Nevada and Ohio.
The native of Long Beach, California, played linebacker at Air Force and began his career at his alma mater in 1989.
New Cal coach Justin Wilcox on Monday announced the hiring of two assistants: Marques Tuiasosopo as quarterbacks coach/passing game coordinator; and Gerald Alexander as defensive backs coach.