The new restaurant will be located within the St Pancras Renaissance Hotel in Kings Cross and will be a reimagining of the original 19th century St Pancras ticket hall.
It will replace the previous Booking Office bar and restaurant.
The 120-cover space will house eight 8-metre tall palm trees and three pendant lights made up of 267 brass leaves each, along with a 22-metre long bar that surrounds the original ticket office.
Powell, who is head chef at Allegra at The Stratford hotel, which is part of the same group as the St Pancras Renaissance Hotel, has created an all-day style a la carte menu of classic dishes finished with a modern twist.
Dishes will include fried chicken, yoghurt and lime; barbecued carrots, braised grains, yoghurt, pistachio and dukkah; fried fish sandwich with spicy tartar sauce; slow roasted lamb shoulder cooked in chermoula spices; monkfish and potato curry with spinach, spring onion and lime; and blackberry trifle.
The venue will also have a raw bar serving items such as oysters and sashimi-style tuna skewers.
Booking Office 1869 will open until 12am on weeknights, and 1am on Fridays and Saturdays.