"I'm really looking forward to being part of the team to try and move the club up the table," Kinsella told the club's official website.
"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."