Crossley left the Spireites in April 2013 when then-manager Paul Cook reshaped his backroom team. He has since been working at Sheffield Wednesday’s academy and most recently at Oakwell.
The 45-year-old is the first addition to new boss Dean Saunders’ coaching staff, with the pair having worked together at Nottingham Forest and with the Wales national team.
Crossley takes over from Eric Nixon, who left Chesterfield on Wednesday along with first-team coach Kevin Lynch and fitness coach Shane Nicholson.
Crossley admits it was an easy decision when his old team-mate offered him the chance to rejoin the Spireites, and said: “I had a great time during my previous spell at the club and I’m delighted that Dean has offered me the chance to come back.
“I’ve already got a head start, having worked with Tommy Lee and Aaron Chapman before. I’m looking forward to working with them again. It’s also great to be linking up with Dean again because I know how hard he works.”