The vastly experienced 61-year-old has been installed as assistant coach just weeks after leaving League One Reading, where he had been working as assistant manager to Leam Richardson.
Kelly had cited family reasons for stepping away from the Royals, where he had worked for the last six months.
The Midlander was part of the coaching set-up at Bury in 2019 when they won promotion from League Two, and it was at Gigg Lane that he first worked alongside Schumacher and his assistant Mark Hughes.
He has more than two decades of experience on his CV and, along with caretaker spells at Preston North End, Sheffield Wednesday, Nottingham Forest, Wigan Athletic, and Barrow, he also stepped up from an assistant’s role to manage Leicester City in 2006 for a one-year spell.
Kelly has also worked with new Under-21s boss Julian Darby at both Preston and Forest, and part of his remit will help bridge the gap between academy and first team.
Schumacher has welcomed the appointment, telling the club: "Rob is somebody I’ve known and respected in coaching for a long time now, and he has been a huge part of my coaching journey.
"He was part of the staff at Bury when I first came into the first-team environment, and I learned so much from him.
"Going into the Championship, having a senior member of staff who has been in there, seen it and done it, and worked at the top level is good for me, Mark and Richie, who are all young coaches.
"He’s a brilliant addition to our coaching staff and I’m glad to have him.
"We’re trying to step everything up a level this year.
"The individual work we do, the unit work we do, and the level of detail the players will receive because we’re competing in the Championship, all of it is greater.
"Having that extra pair of hands matters, but it’s not just an extra body.
"It’s somebody who’s going to add real value.
"He’s a great fella with a great personality, and there aren’t too many people in the game who’ll have a bad word to say about Rob Kelly.
"I’m pleased to bring him onto the coaching staff, and for me, he’s the perfect appointment at this stage in my career and one I felt I needed."