Charlton terminated the contract of Iain Dowie following a review of the management team's performance so far this season.
The Addicks announced on their website that former Crystal Palace boss Dowie, 41, had left the club.
Les Reed has been promoted to head coach, with Mark Robson now working as his assistant, although there was no confirmation from the club as to whether this was a temporary or permanent solution.
Club chairman Richard Murray said: "Over the past two weeks we have conducted a review of the structure we put in place during the summer which involved all senior football management staff.
"The results of this review have, we believe, left us with little option but to act in the manner we have.
"Crucially we had to consider whether we believed our current situation would improve and we reluctantly came to the conclusion that it would not.
"In the situation we find ourselves in, it is also vital that everyone works as a team. Unfortunately, I have to say that has not been the case."
Charlton are bottom of the Premiership, with two wins and two draws from their 12 games so far.
Murray added: "One of the key features of our club during my time as chairman has been stability. It is something I feel is essential in all successful businesses.
"It goes without saying, therefore, how hard it was after only 12 Premiership matches to reach the decision we have.
"By committing some £11.2million on new players in the summer we believe we demonstrated our support for Iain Dowie, as we have also done by backing him with the malicious legal action initiated against him by (Palace chairman) Simon Jordan.
"What we need at this time is as little disruption as possible and accordingly the club has promoted Les Reed to head coach and Mark Robson to assistant head coach.
"Both have a solid Charlton pedigree and I am confident they will do everything within their power, together with the players, to turn our season around."
Dowie took up the reins at The Valley in controversial circumstances, having just left south London rivals Crystal Palace.
Speculation has already begun over who will succeed Dowie, with former England coach Glenn Hoddle the favourite with some bookmakers.