Jose Mourinho has been officially confirmed as Manchester United manager and has signed a three-year contract.
He replaces Dutchman Louis van Van Gaal, who was dismissed on Monday, two days after the club’s FA Cup win.
“Jose is quite simply the best manager in the game today,” said United executive vice-chairman Ed Woodward.
Mourinho, 53, said: “To become Manchester United manager is a special honour in the game. It is a club known and admired throughout the world.”
He said he had always “felt an affinity with Old Trafford” and claimed he has “always enjoyed a rapport with the United fans”.
He added: “I’m looking forward to being their manager and enjoying their magnificent support in the coming years.
“There is a mystique and a romance about it which no other club can match.”
Mourinho has been out of work since being sacked as boss of Premier League rivals Chelsea in December.
“His track record of success is ideal to take the club forward,” said Woodward.
“He has won trophies and inspired players in countries across Europe and, of course, he knows the Premier League very well, having won three titles here.”
The Portuguese’s appointment followed three days of talks between his agent, Jorge Mendes, and senior United officials.
He has already been linked with a move for Sweden striker Zlatan Ibrahimovic, who played for him at Inter Milan.
Ibrahimovic, who has decided to leave Paris St-Germain, told reporters on Thursday that Mourinho “is the man” to bring United “back to the top”.
The BBC reported on Saturday, within an hour of United’s 2-1 win over Crystal Palace, that Van Gaal would be sacked and replaced by Mourinho.
Talks, which started on Tuesday and were delayed by negotiations over Mourinho’s image rights, finally concluded on Thursday.
As well as his three Premier Leagues, Mourinho has led Real Madrid to the Spanish title in 2012, and guided Porto and Inter Milan to Champions League victories in 2004 and 2010 respectively.
However, he left the Blues in turmoil only seven months after winning the Premier League title, with the club 16th in the league, just one point above the relegation zone, having accused some players of “betraying” his work.
Mourinho’s first match at Old Trafford will be on 5 June for Soccer Aid, managing an England team against a Rest of the World side led by Leicester boss Claudio Ranieri.
He will then come up against Guardiola, who takes charge of Manchester City, during a pre-season tournament in Beijing on 25 July.
Mourinho was manager of Real Madrid from 2010 to 2013, winning one La Liga title, while Guardiola was coach of Barcelona.
“We will undoubtedly have fun,” journalist Graham Hunter told BBC Radio 5 live. “I hope we get the quality of football, drama, theatre that we got then. A very different situation coming your way in Manchester next season.”