The airline will operate daily flights to Miami, up from four-weekly services to Fort Lauderdale last summer and five-weekly services to San Francisco.
The change in airport destination reflects customer demand and the increased cargo capabilities these airports offer Norwegian Cargo.
Norwegian will have 32 Boeing 787 Dreamliner aircraft in its fleet by the end of 2018 which are operated on its long-haul routes.
Norwegian serves more destinations in the USA nonstop from Gatwick Airport than any other airline.
Matthew Wood, senior vice president, commercial, at Norwegian said: “We are delighted to meet the strong demand for our transatlantic flights by announcing that Miami and San Francisco will join our summer 2019 flight schedule.
“By also increasing frequency on popular routes next summer, we will provide customers with more choice, smoother connections and exceptional value at affordable fares across Europe, the USA and South America.”