Due to launch in time for the hotel’s 150th anniversary in 2015, the investment is the largest since the hotel's £80m refurbishment in 2009.
The three new areas to be introduced include the Regent Wing, the Langham Club Lounge and the Sterling Suite.
The Regent Wing will comprise 46 rooms and suites and a private four-bedroom apartment, all of which will have access to a private door leading directly to the top of Regent Street.
The Langham Club Lounge will feature an adult only Drawing Room and a Library with a Writers’ Corner, as well as a private check-in and check-out desk and a personal concierge.
Also included is two hours use of the hotel’s private events space, The Loft.
The 450sqm Sterling Suite, which will be unveiled in April 2015, will include six bedrooms, a private butler service and a private media lounge.