Roland Duchatelet's ownership of Charlton is at an end after East Street Investments completed a takeover of the Championship club.
The deal was announced for the first time at the end of November and was subject to approval by the English Football League.
Outgoing owner Duchatelet had been trying to sell the club since 2017.
His reign has been marked by a fractious relationship between himself and the some of the London club's fans.
Duchatelet said: "It was vital for the long-term health of Charlton Athletic that this deal was completed at the very start of the January transfer window.
"It allows the new owners to commit resources to the football side in order to bring in new players who will help secure the club's position in the Championship.
"This is a hugely exciting time for everybody involved with Charlton Athletic and I believe the club is in safe hands with His Excellency Tahnoon Nimer, Matt Southall and Jonathan Heller."
The deal was initially announced in November and new chairman Matt Southall said: "Since our last statement on November 29, it has been my privilege to attend every game and see for myself why this football club means so much to so many people.
"I have met hundreds of fans, attended some of the club's community schemes and spoken with people for whom Charlton Athletic means everything.
"This is a great opportunity for ESI and we are thankful to Roland Duchatelet and his team for giving us the chance to build on such strong foundations.
"Now, for us, the hard work begins. We already have plans in place to support Lee (Bowyer, manager) and his staff over the next month.
"But most importantly is strengthening our links with both the fans and the Charlton community, so they may understand our short and long-term plans for the club and how we intend to build on the amazing support and goodwill already shown to ESI."
Charlton are currently 19th in the Championship with just one win from their last four matches.