Kyril Louis-Dreyfus has completed his takeover of Sunderland after the deal was approved by English Football League on Thursday.
The 23-year-old Frenchman, who becomes the youngest chairman in English football, said he was "proud to become a custodian of this esteemed institution, but I also recognise the significant responsibility that comes with it."
Louis-Dreyfus said that although the club faced "challenges", he was "confident" he could bring "sustainable and long-term success to the club."
Kyril is the son of the late Marseille owner Robert Louis Dreyfus and heir to a multi-billion- pound fortune.
His mother is the chairwoman of agricultural commodities giant Louis-Dreyfus. According to Forbes magazine, she is worth more than $5 billion.
The club announced on Friday that chief executive officer Jim Rodwell has stepped down from his role.
In a statement, Sunderland said Rodwell came to Wearside "with the express task of ensuring that Stewart Donald’s pledge to sell the club was executed as swiftly and responsibly as possible.
"Following the sale of a controlling stake to Kyril Louis-Dreyfus in December, and the subsequent approval by the EFL, that task has now been successfully completed."
Rodwell said "fans can look forward to a bright future" under Louis Drefus' ownership, "whose family have a stellar track record in football club ownership."
Speaking on Thursday, Louis Dreyfus said the takeover marked the start of an "exciting new chapter."
Stewart Donald, Juan Sartori and Charlie Methven will each retain a minority shareholding in the club.
Louis-Dreyfus said: “I would like to thank Stewart, the Board of Directors and the EFL for their diligence and support throughout the recent process.
Stewart Donald said: “I am delighted to welcome Kyril Louis-Dreyfus to the club as our new chairman and controlling shareholder. Kyril’s commitment, acumen and integrity convinced us to accept his proposal.''
"I am proud to say that we have achieved what we set out to in terms of SAFC’s finances – the club is debt-free, was breaking even prior to the pandemic and has retained its Category One Academy status.
''However, it is no secret that – despite spending the highest transfer fees and playing wages in League One history – progress on the pitch has not followed suit.
"That has been a bitter disappointment for us as owners, and we can only apologise for falling short in this regard.
“Whilst we certainly made mistakes, everything was done with the best of intentions with the view to deliver this aim, but we just fell short and in football, unfortunately, a miss is as good as a mile.''
The news comes after the Black Cat's reached a second EFL Trophy final in the three season's they've spent in the third tier.
Lee Johnson's men beat league leaders Lincoln City in a penalty shoot-out. Sunderland will head to Wembley to take on League Two side Tranmere on Sunday, 14 March.