The versatile French international, who has 41 caps, finalised his transfer from Milan at the World Cup centre in Paris. He said he was looking forward to the challenge of playing in the Premiership after five years at San Siro. "I'm happy and it's an important thing in my career to go and play in England," he said.
"It was a big decision to leave Milan but Chelsea are in the Cup-Winners' Cup and they are a club that's growing."
Desailly, who can play in midfield or defence, represents the third major summer investment by Chelsea's manager, Gianluca Vialli, and underlines the London club's determination to add the Premiership crown to their collection of cups from last season.
Pierluigi Casiraghi began the latest continental drift towards Stamford Bridge when he arrived as a club record pounds 5.4m transfer from Lazio. Ferrer has a wealth of experience, adding 35 international caps to a medal haul that includes five Spanish championships, the European Cup and two CupWinners' Cups. He has appeared 330 times for Barcelona.
Ferrer and Chelsea concluded negotiations at the Spanish World Cup training base in Chantilly. "I've played in the Champions' League but this will be a new experience for me and I think that experience will be very successful," he said.
Martin O'Neill, who has spent the last week thinking over his future, has 48 hours to quit as manager of Leicester City - or Everton will look elsewhere for a manager.
The Irishman is aware that the Goodison club are involved in a long and protracted process of sacking their manager, Howard Kendall, and the job would appeal to him. However, the Merseysiders also need to know O'Neill's plans quickly or they will move to install an alternative replacement, with the Manchester United No 2 Brian Kidd and the former Celtic manager Wim Jansen two possible targets.
Meanwhile, Peter Johnson, the beleagured Everton chairman who has won himself more criticism by leaving Kendall in the dark about his future, will head for a World Cup break in the South of France this weekend in what is seen as an indication of his confidence in landing O'Neill.
The Southampton manager Dave Jones has opened negotiations to sign the French striker, David Zittelli, from the German side, Karlsruhe. The player is out of contract this summer and will fly to England for talks over a free transfer next week.
Jones has been given pounds 10m to spend on strengthening his squad and needs to bring in a striker after last week's pounds 7.25m sale of Kevin Davies to Blackburn Rovers.
Jones is also tracking the Belgian international Lokonda Mpenza from Standard Liege and has held talks with the Newcastle defender Darren Peacock and Tottenham's David Howells.
Saints have also expressed an interest in signing the Blackburn winger Stuart Ripley and Empoli's pounds 5million-rated striker, Carmine Esposito.
The Belgium and Excelsior Mouscron defender Gordan Vidovic said yesterday that he is close to signing a three-year contract with Aston Villa for around pounds 430,000.
Sheffield United have told Newcastle that they are not prepared to sell their pounds 2m-rated defender Wayne Quinn until they have appointed a new manager. Reading are waiting to hear if Manchester United's reserve midfielder Grant Brebner will join them, while the Football League newcomers Halifax Town have appointed Chris Holland to succeed John Stockwell as chairman.