The new Real Madrid player, who came close to signing for Caen when he was younger, has acquired 80 percent of the shares through Coalition Capital, the investment entity of Interconnected Ventures, replacing US investment fund Oaktree as majority shareholder.
No figure has been released officially but French media reports put the acquisition fee at 15-20 million euros ($16-21.6 million).
"This transaction marks a significant step in the club's strategic development and reinforces its natural ambition to remain one of the most successful clubs in French football," the club said in a statement.
"This acquisition will provide Caen with additional strategic resources to strengthen its sporting policy, modernise its infrastructure and develop innovative projects."
Mbappe's close friend Ziad Hammoud will take over as chairman of the club.
"We are determined to create an environment where young talent can flourish and where the club can defend its identity with strength and ambition," Hammoud said in the press release.
The 25-year-old World Cup winner, who now becomes one of the youngest owners of a professional club, was courted by Caen when he was just 13, before he joined Monaco and then Paris Saint-Germain.
"You'd have to think that the time he spent at Caen in his youth left its mark on him! How proud we are to see a champion like @KMbappe investing in @SMCaen," the mayor of Caen Aristide Olivier posted on social media.
Founded in 1913, Caen finished fifth in the top flight in 1992 and reached the League Cup final in 2005 but have played in France's second tier since 2019.
