The 125-year lease of the historic building on Regent Street was bought by Georgi and Alfred Akirov for £90m at the end of 2008 when it was being run as a conference and banqueting venue by Starwood Hotels and Resorts.
David Chipperfield Architects and Donald Insall Associates were brought in to restore the building to its former glory and turn it into a luxury hotel and spa with two restaurants - The Grill Room and The Domino Room; bars - The Bar and Ten Room Lounge and the Café Royal Café. The hotel will also offer a members' club.
"The comprehensive works have sensitively restored the listed interiors dating from the 1860s and 1930s whilst simultaneously creating a visually stunning 159 room luxury hotel and spa that is at once totally contemporary and referential to its illustrious past," said a statement from the hotel's owners.
It will open its doors in June with former Millennium Mayfair Hotel general manager Louis Sailer as general manager and will form part of The Set, a collection of 'beautiful and contemporary' hotels which includes The Conservatorium in Amsterdam and Lutetia in Paris.
Cafe Royal first opened its doors in 1865 and has been host to a number of influential figures, including Oscar Wilde, Winston Churchill and Princess Diana.
Original furnishings and contents from the building were auctioned off when it last closed its doors in 2008.