New Scotland Yard, as it is known, has been taken over by the Abu Dhabi Financial Group for a 120 million pounds over the asking price.
The building on Victoria Street in Westminster has been the headquarters of the Metropolitan Police since 1967.
Its famous rotating sign will move to its new headquarters in the Curtis Green building on Victoria Embankment.
London Mayor Boris Johnson said, "This landmark deal allows us to preserve the past whilst giving today's Met a vital cash boost".
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When completed in 2016, the restructure will save London's police force more than 60 million pounds in annual running costs - enough to fund 1,000 officers, the mayor's office added.
Met Commissioner Bernard Hogan-Howe said, "We now expect to need to be making savings of up to 1.4 billion pounds by the end of the next spending review, including some 600 million pounds which we will have delivered by 2015-16. This is equivalent to a third of the Met's original budget so this money is absolutely vital to us".