Knowles, the Blue Devils' defensive coordinator since 2010, replaces Glenn Spencer, who was fired as the Cowboys' defensive coordinator earlier this month.
Under Knowles last season, Duke ranked third in the ACC in scoring defense and fourth in total defense.
Before arriving at Duke, Knowles was the head coach at Cornell, his alma mater.
Proud to announce six new members of the Oklahoma State family. #GoPokes #okstate— Mike Gundy (@CoachGundy) January 29, 2018
Shane Eachus (Ursinus College)
Jim Knowles (Duke)
Greg Richmond (Fairmont State)
Brian Rock (Holy Cross)
MK Taylor (Jacksonville State)
Chris Thurmond (Formerly Rice) pic.twitter.com/uqUAWuYgYa
Besides Knowles, Gundy announced five other additions to his staff, including Ursinus College defensive coordinator Shane Eachus.