New City boss Stuart Pearce wanted Harford to be his assistant manager but after recently being appointed as boss of Rotherham, Harford is staying with the Millers.
Harford joined Forest during the season just finished to work alongside Joe Kinnear and took over on a caretaker basis before Gary Megson's arrival at the club.
Pearce is now set to turn his attention to former team-mates Nigel Clough and Des Walker as he puts his backroom team in place.