The shock deal that has taken Chelsea fans and the football world by surprise was finalised on Tuesday night.
Mr Abramovich, 36, is offering 35 pence a share and has already agreed to buy 84,908,506 shares of Chelsea Village - the company which owns the football club.
Maverick chairman Ken Bates, the man who bought the club for 1p way before the football boom and has 50 million shares, will be richly rewarded for his efforts.
But it will mean the cantankerous grandad of English football will take a back seat at the club he loves: the Stamford Bridge chairman has agreed to sell his £17.5million stake.
In a statement Bates said: "This is a great deal for Chelsea Village, the club and its fans.
"In today's highly competitive football market, the club will benefit from a new owner with deeper pockets to move Chelsea to the next level.
"I look forward to working with Roman Abramovich to achieve even greater things.
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| Chelsea: Sold to a Russian | |
However, Chelsea fan Tony Banks MP said that he had serious concerns about the deal.
"I want to know if this individual is a fit and proper person to be taking over a club like Chelsea and until that question is answered, I'm afraid the jury is out," he said.
"I would have preferred that the takeover of Chelsea had taken place after these questions had been answered rather than leave us in the situation we are in.
"We know that Chelsea is in financial difficulties and that a deal has been arranged with an individual we know nothing about, with a background we know nothing about, from a country that has a reputation that is not savoury in terms of its financial situation."
Last season Chelsea finished fourth in the Premiership and qualified for the European Champions League.
Mr Abramovich said in a statement: "We are delighted to agree this deal to acquire what is already one of the top clubs in Europe.
"We have the resources and ambition to achieve even more given the huge potential of this great club."
Mr Abramovich is one of the major shareholders in Sibneft, one of Russia's largest oil companies, and a close friend of Russia President Vladimir Putin.