The 55-year old has departed Crawley to take the reins at Forest, replacing Steve Cotterill, and was quick to thank the League One club for their assistance since he took over from Steve Evans in May.
"I would just like to take the opportunity to thank everyone at Crawley Town," he said.
"I have been made very welcome by the staff and players and was looking forward to the new challenge of establishing the club in League One.
"As you can appreciate, opportunities like this one with Nottingham Forest don't come along too often. I appreciate Crawley Town's integrity and professionalism in dealing with the matter and allowing me to take up this new challenge.
"I wish Crawley Town every success for the future and I'm sure the club will continue to go from strength to strength."