Roofnic, a 100-cover offering, is set to run until September when it will be replaced with a winter pop-up launching in the autumn.
Inspired by the idea of a rooftop picnic, the menu features a selection of small plates, including Pulled Pork Tacos; and Butterfinger Cookie Dough Cheesecake, alongside healthy juices, cocktails, and affordable wines and prosecco.
The site has been developed with £40,000 of funding won by Marriott restaurant general manager Ashley Dawes and senior marketing executive Stacey Plaine, following an internal competition to transform the disused space.
Located on the fourth floor of the hotel, it will be accessible via a secret entrance on Oxford Street near Marble Arch.
Roofnic will open seven days a week from 10am-10pm at 535 Oxford Street.