The 345-room property, close to Victoria station, will be renamed the Amba Hotel Victoria after a conversion by its owner-operator glh hotels in 2019.
Its restaurant, The Grosvenor Arms, and Tea Lounge have already been revamped and are open to the public.
Additional food and beverage outlets, bedrooms and event spaces will be redesigned throughout next year, with the hotel remaining open throughout the process.
Neil Gallagher, chief executive of glh, says the Amba brand was designed to 'raise expectations of a four-star hotel' and that the new-look Grosvenor will offer an 'upgraded hotel experience'.
The first Amba property opened in Charing Cross in 2014, followed by a second in Marble Arch in 2015.
Glh operates 17 London properties, including The Royal Horseguards Hotel and several Thistle-branded sites.