The 64-cover venue will replace the hotel's existing Razzi restaurant and feature a menu championing local Welsh produce.
Head chef Mark Freeman's dishes will include the ‘Grey’ Croque Monsieur; Honey Glazed Welsh Lamb Shank Bubble ‘n’ Squeak; and a Lobster Club Sandwich.
A locally-stocked bar is set to feature spirits from the Cardiff Gin Company and craft beers from Welsh breweries.
Marie Fagan, general manager at Hilton Cardiff, said: “We’re very excited about the opening of Grey, it will be a fantastic addition to the area and we can’t wait to welcome our first guests in September."
Freeman joined the hotel in 2012 after working at the Laguna Kitchen & Bar at Cardiff’s Park Plaza Hotel.
Grey will open seven days a week from 26 September.