Reid, a former consultant chef at The Vineyard Group and executive chef at the St Pancras Grand, joined the hotel's Oak Room restaurant in November after executive chef Adam Simmonds left open his own restaurant.
In his new role, Reid, who has also worked at Northcote, L'Escargot and The Belvedere in Holland Park, will oversee a team of 22 chefs working across two restaurants and a busy events business and is planning to develop a training scheme for them.
He said: “I am very much looking forward to the challenge of steering Danesfield House Hotel & Spa forward and I am particularly keen to build a strong training and development ethic with the team.
"With two restaurants and a busy events business the variety is here to develop a wonderful training environment for young chefs”
Classically-trained Reid is not planning to make any changes to Danesfield House's two restaurants - the formal Oak Room and more relaxed The Orangery, but will continue to deliver a modern British menu using simple ingredients.
The Oak Room will open Thursday to Saturday for lunch and Tuesday to Saturday for dinner. Lunch is priced at £23 for two courses or £29 for three courses and dinner is £55 for three courses.
Danesfield House general manager Anthony Cox said: "Billy is highly regarded in the trade for his approach and has cooked in some brilliant kitchens over the years, so I am particularly pleased to bring him to Danesfield House.”
Situated in a country mansion between Marlow-on-Thames and Henley-on-Thames, Danesfield House Hotel & Spa opened for business 20 years ago and has built up a strong reputation for its cuisine through its two restaurants ever since.
Simmonds was executive chef at the 87-bedroom hotel for seven years before departing to open his own restaurant in London.