Chelsea's new owner Todd Boehly promised to build on the team's "remarkable history of success" after the American completed his takeover of the Premier League club on Monday.
Boehly's consortium agreed a deal to buy Chelsea from Roman Abramovich for £4.25 billion ($5.3 billion) on May 7 and the sale has now been officially rubber-stamped.
"We are honoured to become the new custodians of Chelsea Football Club. We're all in, 100 percent, every minute of every match," Boehly told Chelsea's website.
Boehly's takeover ends Abramovich's 19-year reign as Chelsea owner after the Russian put the club up for sale in March.
Abramovich was sanctioned by the British government for his alleged links to Russian President Vladimir Putin following the invasion of Ukraine.
Los Angeles Dodgers co-owner Boehly has set his sights on emulating Chelsea's success during the Abramovich era, which included five Premier League titles and two Champions League crowns among 19 major trophies.
"Our vision as owners is clear: we want to make the fans proud," Boehly said.
"Along with our commitment to developing the youth squad and acquiring the best talent, our plan of action is to invest in the club for the long-term and build on Chelsea's remarkable history of success."
Chelsea had been operating under a special government licence which would have expired on May 31 if Boehly had been unable to seal the purchase.
That would have put Chelsea's future in doubt, but they are now able to look forward to next season as the Boehly regime takes the keys to Stamford Bridge.
Boehly's group needed approval from the Premier League, the British government and Portuguese authorities -- Abramovich has Portuguese citizenship -- before the sale could be completed.
"I personally want to thank ministers and officials in the British Government, and the Premier League, for all their work in making this happen," Boehly said.
Boehly fought off 11 rival bidders to buy Chelsea in what is a record sale for a sports club.
He will "share joint control and equal governance of the club" with his main partner Clearlake Capital investment firm.
Boehly is Chelsea's controlling owner, but will work closely with Clearlake co-founders Behdad Eghbali and Jose Feliciano.
Swiss billionaire Hansjorg Wyss and US tycoon Mark Walter are the other main members of the consortium.
"We are excited to commit the resources to continue Chelsea's leading role in English and global football, and as an engine for football talent development," Eghbali and Feliciano said in a joint statement.
"We also want to thank the authorities for all their work throughout the process.
"As pioneers in sports and media investing, we are thrilled to partner with Todd and the rest of the consortium to meaningfully grow the club as a global platform.
"Together, we will expand the club's investment across infrastructure, technology, and sports science to support the incredible Chelsea football and commercial teams - all with the goal of leveraging this growth to fuel even more on-pitch success."
Boehly's arrival in west London will turn the page on Chelsea's remarkable transformation from underachievers to serial winners under Abramovich.
Crucially, the takeover completion should give Blues boss Thomas Tuchel the financial support to mount a challenge to Premier League champions Manchester City.
Chelsea finished third in the Premier League this term, ensuring they qualified for next season's Champions League.
Tuchel's side also reached the FA Cup and League Cup finals -- losing both matches to Liverpool on penalties -- and won the Club World Cup and UEFA Super Cup.
Chelsea were unable to sign players or offer contracts to existing stars because of the sanctions on Abramovich.
They are set to lose Antonio Rudiger to Real Madrid on a free transfer, while Andreas Christensen is set to join Barcelona when his contract expires in the close-season.
After Abramovich halted plans to redevelop Chelsea's stadium several years ago, the new owners "are committed to investing in key areas that will extend and enhance Chelsea's competitiveness, including the redevelopment of Stamford Bridge".