The Americans have paid around £400m to buyout majority shareholder Farhad Moshiri.
An agreement had been struck on September 23, but the deal was waiting for Premier League approval.
Chairman Dan Friedkin has a net worth of £6.16bn according to Forbes and the Group also own AS Roma.
Marc Watts, incoming Executive Chairman of Everton Football Club, declared: "Today marks a momentous and proud occasion for The Friedkin Group as we become custodians of this iconic football club. We are committed to leading Everton into an exciting new era both on and off the pitch.
"Providing immediate financial stability to the Club has been a key priority, and we are delighted to have achieved this. While restoring Everton to its rightful place in the Premier League table will take time, today is the first step in that journey.”
Moshiri also stated: “I truly believe that the transaction with The Friedkin Group is the best outcome for the Club and its future success. There has been a huge team effort in getting to this stage and I would like to personally thank my Board colleagues John Spellman and Colin Chong and all the senior management team including Katie, James, Richard and of course Kevin and Sean for their huge commitment to the Club.
"Despite a challenging geopolitical backdrop, a significant amount has been achieved over the last couple of years including the delivery of a new sporting department, the stabilisation of our finances and the delivery of our iconic new stadium. I now hand over to new owners confident in the outlook for the Club and that our incredible fans will see the success on the pitch that they so thoroughly deserve.”