Chesterfield's assistant manager Alan Knill is the new manager of Bury and takes up his new appointment immediately.
He was given permission to talk with the Shakers last month and, as a former Bury player, there has been growing speculation that he was one of the favourites to take on the vacant manager's position at Gigg Lane.
The former Rotherham United manager joined the Spireites in March 2007 in a coaching capacity before being appointed assistant manager.
Chesterfield manager Lee Richardson said: "I am both disappointed to lose Alan yet pleased that he has this chance to get back into football management. We wish him well and I thank him for his support whilst at Chesterfield."
Lee Richardson added: "As I have been aware of this developing situation, contingency plans are in place. I have lined-up a replacement and expect to make an announcement later today."