The Covent Garden site shut its doors on 28 August and will reopen for dinner on 12 September.
The restaurant is adding an extra 10 covers to the dining room, taking it to 67-covers in total, and four seats for walk-ins at the entrance.
It is also creating a bespoke waiters’ station and placing a screen near the door to protect diners from the breeze.
“This is quite a big thing for us because a lot of people complain that they can’t make reservations or get a booking,” Frenchie’s general manager David Durban told BigHospitality.
“Around peak times we are pretty much always full or nearly so. We knew that the kitchen could cope with extra availability but just didn’t have the space to do so until now.”
Durban added that he and Marchand are also developing the restaurants pre-theatre menu, though there is currently no timescale on when the new dishes will launch.
Marchand was nicknamed ‘Frenchie’ by Jamie Oliver while working at the chef’s Fifteen restaurant in London, and used the name for his debut Paris restaurant and wine bar when it opened in 2009.
The chef returned to London to open the sister Covent Garden site in 2016, and the restaurant was ranked 37th in the Estrella Damm National Restaurant Awards top 100 list 2017.
Frenchie is now taking bookings for dinner on the 12 September.