The chef, who, with business partner Nigel Platts-Martin, sold The Square to MARC earlier this year, plans to cook at the restaurant when it opens in September.
He said: "I still have unfinished business with food, and am incredibly excited to be returning to the heart of a kitchen.”
The 64-cover restaurant, named Elystan Street, will be redesigned by Clare Nelson Design before re-opening. It will serve a modern British menu with 'clean, ingredient-led dishes full of natural vitality' and open for lunch and dinner.
"The aim will be, as it always has been, to give great pleasure," said Howard.
Mascarenhas and Howard co-own Kitchen W8 in Kensington and Sonny’s Kitchen in Barnes.
The restaurant site at 43 Elystan Street was home to Aikens' eponymous restaurant until January 2014.