Mr Gates, the founder of Microsoft, and two other partners in an American syndicate have bought the famous building for pounds 44m.
The consortium has bought Cliveden plc, the luxury hotel group that leases the house from the National Trust. They will also take control of the Royal Crescent Hotel in Bath, the Cliveden Town House in Knightsbridge, and a new hotel being built in Edinburgh.
The move will fuel speculation that Mr Gates is planning to move to England. He recently purchased a house in the Notting Hill are of west London for pounds 8m.
Cliveden is an impressive building in a commanding position on cliffs high above the Thames near Maidenhead in Berkshire. It dates back to 1666, although almost all of it is more modern, having been updated several times. The 400-acre landscaped gardens stretch down steep slopes to the banks of the river.
As grand country piles go, Cliveden has seen more than its fair share of revelry over the years. When Lord and Lady Astor owned the house, they entertained such guests as Edward VII, and the authors Rudyard Kipling and Henry James.
For the past 15 years the house has been a hotel, charging guests up to pounds 750 per night for the luxurious Lady Astor and Prince of Wales suites, and pounds 235 for smaller double rooms.
Although owned by the National Trust, which acts as its landlord, Cliveden plc occupies the estate on a 100-year lease. On their takeover, Bill Gates and his business partners in the venture will automatically inherit the lease and it is believed the building will continue as a hotel.
The National Trust has the final say on structural works to Cliveden, and the hotel chain has also in the past consulted them on decorative matters. "We trust the same arrangement will continue with whoever is buying he lease," said a spokeswoman.
Cliveden plc yesterday confirmed that the deal was on the table. Already 25 per cent of the shareholders have agreed to it and the group is encouraging acceptance from other shareholders to get the minimum 50 per cent needed to push the deal through.
The National Trust said it knew negotiations were under way for a new buyer for the lease but did not know with whom. A spokeswoman said yesterday they had not been informed of the bid by Bill Gates and his associates and only knew of it through news reports.