The routes will be altered as of March 31 next year with prices leading in at £174.90 one way.
Flights to Miami will be offered on a daily basis as opposed to the four-weekly service to Fort Lauderdale while San Francisco flights will be available five times a week.
The airline said the change in airports has come about thanks to a combination of customer demand and increased cargo capabilities at both the east and west coast facilities.
The change means the airline will also continue to offer 13 long-haul routes from the UK with Brazil also making its debut appearance with flights launching to Rio de Janeiro, also on March 31.
However, some frequencies are also being cut for next summer with the Los Angeles route will reducing to a daily service while the Chicago route will reduce to four flights per week.
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 Rio de Janeiro as part of 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.”
Gatwick airport head of airline relations Stephen King said: “These new Miami and San Francisco routes will fly passengers straight into the heart of two of America’s most iconic city destinations.
"In all, Norwegian will fly to 11 US destinations from Gatwick next summer, which gives passengers both tremendous choice and exceptional value as the airline offers some of the most competitive long-haul airfares around.”