Mark Kinsella has been appointed development coach at Charlton.
Kinsella made 226 appearances for Charlton between 1996 and 2002
The 34-year-old has quit his role as reserve-team manager and first-team coach at Walsall to join new manager Les Reed's backroom staff.
"I'm really looking forward to being part of the team to try and move the club up the table," the former Addicks captain told the club website.
Kinsella combined playing with his coaching duties for Walsall and will be available to play on Saturday.
"Walsall have been brilliant to me," he said.
"I've really enjoyed my time at the club and that has made it a much harder decision than it might have been.
"But they know how I feel about Charlton, which is my club. It's difficult to leave, but I'm very excited about coming back to Charlton."
Mark has very strong leadership qualities, tremendous drive and enthusiasm
Walsall chairman Jeff Bonser explained that Kinsella had a clause in his contract allowing him to join a Premiership club should the opportunity arise.
"Charlton approached the club earlier this week in order to gain permission to speak to Mark and, in line with our agreement, permission was granted," said Bonser.
"We explained to Charlton that Mark was an important part of our plans but, at the same time, we could not stand in his way.
"We are grateful to them that, despite his imminent departure, they were prepared to allow him to play at Bury on Tuesday and, should he be selected, against Swindon this coming Saturday."
Charlton manager Reed was delighted with Kinsella's appointment.
"Mark will be responsible for the development of our young pros, for the liaison with the academy set-up and the management of the reserve team," said Reed.
"I'm particularly pleased that Mark has agreed to join us because he has very strong leadership qualities, tremendous drive and enthusiasm and of course Charlton blood running through his veins.
"It will be a big boost for us to have someone of Mark's quality on the full-time coaching staff, and it's further evidence of our commitment to move forward and upward."