The chef oversaw the site and it was recommended in the Michelin Guide, but it shut its doors on 31 October.
A spokesperson told BigHospitality that the restaurant closed after the ten-year partnership between HIX and Brown's Hotel came to an end.
Hix thanked the restaurant's 'loyal diners and contributing artists' in a tweet.
The news follows the closure of a number of Hix’s London sites over the past five years.
The chef shut HIX Belgravia and Mark’s Bar at the Belgraves Hotel in 2012 and HIX City in Devonshire Square in 2015. His restaurant at Selfridge’s is also no longer trading.
A restructure of Hix Restaurants saw the chef enter in to a joint venture with Westbury Street Holdings (WSH), the owner of cafe chain Benugo and Searcy’s catering company, in April last year.
Hix said at the time that he was looking to expand his restaurant portfolio.
The chef currently operates five London restaurants, including HIX Soho and chicken and steak restaurant Tramshed, alongside three Mark’s Bars.
He also teamed up with artist Damien Hirst to open Pharmacy 2 at the Newport Street Gallery in Vauxhall in 2016, and runs a seafood restaurant and boutique hotel in Lyme Regis.
The former HIX Mayfair site is currently trading as The Restaurant at Brown's Hotel, but will not be without a famous resident for long. The hotel has announced that Heinz Beck, chef at three-Michelin-starred La Pergola in Rome, will host a six-week pop-up in the space from 13 November.
It marks a return to London for Heinz, who ran Apsleys at The Lanesborough Hotel from 2009-13 when the hotel closed for a nearly two-year refurbishment.
Ora will serve signature dishes from La Pergola, including John Dory with curry and red beetroots on a light pesto sauce.
Drinks maestro Salvatore Calabrese will run a residency at the hotel’s Donovan Bar, serving a special Martini and Negroni menu, over the same period.
“I’m excited to return to London and bring with me some of my favourite dishes created at La Pergola in Rome," says Beck. "It’s an honour to serve guests in such an illustrious hotel and I’m sure will be a fantastic six weeks!”