Chef-patron Howard, who has overseen the kitchen at the Mayfair restaurant for 25 years, said he was handing the reigns over to a 'passionate restaurateur'.
MARC chairman Marlon Abela will run the restaurant with all existing staff retained. Sous chef Dan Fletcher will head up the kitchen following head chef Gary Foulkes' departure last week.
Platts-Martin, Howard's business partner and restaurateur behind The Ledbury, Chez Bruce and La Trompette, said: “Phil and I have had a wonderful 25 years at The Square. I am confident that The Square will continue to thrive under the stewardship of Marlon Abela.”
Abela said there were no plans to make any changes at the restaurant, which opened in 1991 and has retained its two Michelin stars for 19 years.
“I am delighted to welcome The Square into our family of restaurants. I have always admired its strong commitment to modern fine dining, devotion to quality and use of the finest, locally-sourced British ingredients,” he said. "The team’s approach to rigorous seasonality, passion for wine and dedication to delivering service excellence is in line with our core values.”