The 300-cover restaurant is one of 32 John Lewis sites being transformed and operated in partnership with contract caterer Benugo under the Platter name by the end of 2027.
Plans for the rollout were first revealed in February, with the Platter brand unveiled in May.
Restaurants have already reopened under the name at John Lewis stores in Bluewater, Chichester and Reading.
The programme, which will see Platter replace John Lewis’s longstanding The Place to Eat brand, forms part of the retailer’s £800m multi-year investment in its stores, brand and customer experience.
Described by John Lewis as “one of the biggest restaurants on Oxford Street”, the fifth-floor venue features an open kitchen serving hand-stretched pizza, a deli preparing food on site and a dessert parlour.
It is not the first time the central London department store has served pizza, with the site having once housed a Rossopomodoro restaurant.
Platter Oxford Street also includes a bar overlooking the store’s atrium and an outdoor terrace with 50 covers.
An in-store roastery will see a master roaster oversee the roasting of a single-origin Arabica coffee sourced exclusively for John Lewis. The coffee will be served in the restaurant and sold as whole beans or ground coffee for customers to take home.
The restaurant is also home to The Residency, a rotating pop-up space. Its first resident is London-based patisserie The Eclectic Collection, which is known for its fruit-shaped desserts.
“This is a real investment in something customers told us mattered,” says Katie Papakonstantinou, director of services and hospitality at John Lewis.
“Sitting down for something to eat and drink has become part of how people shop, and Platter is built for that.
“Whether stopping for coffee, a pizza with family, a treat from the dessert parlour or a drink at the bar, we’ve created a space that makes a shopping trip even more special.”
Platter Oxford Street will sit alongside the retailer’s wider hospitality offer, which includes Benugo, Ori Caffè, Huffkins tea rooms, Jamie Oliver Cafe, 1864 Rooftop and Kamakura.