"Graeme and I have reached an agreement but I had to wait until the Blackburn chief executive returned from his holiday before anything could happen.
"While it saddens me greatly that I have to leave Rangers after six magical years at the club, I'm really looking forward to working with Graeme and Blackburn Rovers.
"This is a new challenge for me and it's one that I'm delighted to take on. I will go on holiday before pre-season training starts to get some rest before the new season."