The two-Michelin-starred chef's restaurant will have a focus on Cornish produce.
It will be located in an orangery overlooking the hotel's garden, with interiors designed by Russell Sage, who created the Goring's lobby and royal suite. A new kitchen has been built below the new restaurant, while the Goring bar is also being relaunched at the same time.
The 60-seat restaurant will provide a more casual dining option to the hotel's Dining Room.
Jeremy Goring, chief executive and the fourth-generation owner of the hotel, said he was inspired to launch a seafood restaurant as a result of his family's strong ties to Cornwall.
He previously told The Caterer: "Some of the best seafood in the world comes from the pristine waters around Cornwall. We're looking forward to bringing this West Country treasure to London, with the help of Nathan Outlaw.
"The restaurant will be all about simplicity on the plate, freshness, and our usual heartfelt British service."
He added that the new restaurant will be "an eccentric, uplifting space" which is being created with "the help of some very special craftsmen and designers".
Dishes on the menu will include starters of cured monkfish, ginger, fennel and yoghurt; and cuttlefish black pudding, apple and kohlrabi; followed by main courses of turbot herbed and battered with warm tartare sauce; and red mullet with devilled shrimp butter and chicory. There will also be a choice of daily specials available reflecting the availability of fresh fish delivered daily from Cornwall.
Desserts will include gooseberry pavlova with custard ice cream and strawberry tart with yoghurt sorbet.
The newly designed Goring bar will serve cocktails featuring herbs sourced from the Goring's gardens, which are being grown with the help of leading herb expert Jekka McVicar.
Popular tipples are expected to include Rosehip Royale (Pimm's No 6 Cup, Sacred Rosehip Cup, Champagne, strawberries, cucumber, mint and rose); and the Madness of King George (King George III's favourite whisky turned into an apple Manhattan).
Bar dishes will range from lobster scampi with chilli and pepper jam to smoked fish platter with horseradish and lemon.
Outlaw's restaurant at the Capital hotel in nearby Knightsbridge closed earlier this year after six years. Beyond London, Outlaw operates two restaurants in Cornwall, including the two-Michelin-starred Restaurant Nathan Outlaw in Port Isaac.