The soft re-branding of the four-star, 331-bedroom hotel, near St James's Park, will be a blow for Accor. The French-based hotel company announced St Ermin's as the first UK hotel to join MGallery - its equivalent brand to the Autograph Collection - two years ago when the hotel re-opened following the arrival of new owners and an extensive refurbishment.
St Ermin's will be the third hotel in the UK to join the Autograph Collection, having announced earlier this month that Threadneedles in London and the Glasshouse in Edinburgh would be joining the brand.
Amy McPherson, president and managing director for Marriott International in Europe, said the addition of St Ermin's in a prime, central London location was "a significant event" and "incredibly exciting time" for the Autograph Collection.
"Our three Autograph Collection hotels in the UK offer travellers an enviable range of artistic, culinary and cultural adventures and this historic hotel is a hugely powerful addition."
St. Ermin's, converted from a Victorian apartment block to a hotel in 1899, was bought by the US property company Amerimar Enterprises, in conjunction with London-based Gracemark Investments and Angelo, Gordon & Co, for £65m in 2010.
The Autograph Collection of 40 independent properties in the United States, Europe, Caribbean, and South America, participate in Marriott Rewards, the company's guest loyalty programme across more than 3,200 hotels in 68 countries.