Russian ex-KGB agent Alexander Lebedev is to buy the London Evening Standard newspaper for the sum of £1.
The paper's publisher - the Daily Mail & General Trust (DMGT) - said it had agreed to the sale of a majority interest in the paper to Mr Lebedev.
The billionaire businessman is believed to have made an offer for approximately a 76% share of the paper.
He has previously revealed that he used the paper to find out information when he was a young spy based in London.
DMGT said the Evening Standard would pass into the hands of Evening Press, a company formed by Mr Lebedev and his son Evgeny Lebedev and owned by Lebedev Holdings.
DMGT's Associated Newspapers division is to retain a minority share of 24.9% in the new firm, called Evening Standard Ltd.
It is the first time a Russian oligarch has owned a British title, but Mr Lebedev said he strongly supports a free press and would not interfere with the paper editorially.
In an attempt to head off any such fears, DMGT said the Evening Standard would establish a new editorial committee to "safeguard the principle of editorial independence".
Mr Lebedev said: "We are strong supporters of a free and independent press and we greatly admire the Evening Standard as an iconic publication with its pedigree of fine journalism and commentary.
"We are committed to strengthening the newspaper's competitiveness and look forward to working with Associated, which will continue to be involved as a minority shareholder."
DMGT chairman Lord Rothermere said the company was "very proud" to have owned the paper.
He said: "It has a long and distinguished history as one of the world's great city newspapers, based on outstanding journalism.
"I believe that Alexander Lebedev shares my commitment to newspapers and will continue to invest in the Evening Standard."
He said none of DMGT's other newspaper publications would be involved in the deal, adding that the company "remains fully committed to journalism and newspaper ownership".
Sir Peregrine Worsthorne, former editor of the Sunday Telegraph, said the take-over was a sign of "national decline".
He told the BBC: "I think it's one more example that we are no more a serious nation that we allow a serious paper to be taken over in our capital by a Russian oligarch.
"Imagine the French having Le Monde or Le Figaro taken over by a Russian multi-millionaire? It's an illustration of how our national pride has declined."
Mr Lebedev's fortune, which is reported to be worth around $3.1bn (£2.1bn), was made mostly through banking, insurance companies and from his stake in the Russian airline Aeroflot.
In 2006, he teamed up with ex-Soviet leader Mikhail Gorbachev to buy shares in the Russian paper Novaya Gazeta and his property portfolio includes a string of boutique hotels across Europe.
BBC media correspondent Torin Douglas has said the Evening Standard had been hit by the advertising downturn and a fierce free newspaper battle in London.
Mr Lebedev has also expressed an interest in buying out other struggling newspapers both in the UK and the United States.
His take-over of the Evening Standard s expected to take place in February following consultation with employees.