Peter Varney is leaving his role as Charlton's executive vice-chairman.
The former Addicks chief executive, who returned to The Valley in December 2010 as part of the takeover of the club by CAFC Holdings Ltd, will step down at the end of July.
He will be replaced by former Umbro senior vice-president Martin Prothero, who will join the Charlton board on August 1.
Chairman Michael Slater said: "Peter always intended to remain on the board for a period of two years after the takeover.
"But, following the club's promotion to the Championship, he has decided to stand down earlier than planned in order that his successor can familiarise himself with the club and his new role during the summer.
"The board respects Peter's decision and thanks him for his part in turning around the fortunes of the club."