The new service, which takes seven hours 50 minutes westbound and seven hours 10 minutes eastbound, is the first-ever scheduled route to the US from North East England.
It commenced on Saturday (23 May) and is available five days a week until 7 September.
The outbound flight departs Newcastle Airport daily (except Wednesday and Thursday) at 9:10am, arriving at New York/Newark at 12:00 noon the same day.
The return flight departs New York/Newark daily (except Tuesday and Wednesday) at 7:20pm, arriving in Newcastle at 7:30am the following day.
David Laws, chief executive at Newcastle International Airport, said: "Passengers are making the most of United’s excellent route network to connect onto numerous further afield destinations. Some travellers are even using the flight to reach Hawaii.
"In addition to UK residents travelling on to North America for business or for leisure, the service makes the North East of England much more accessible for inbound travel from the States, and we are working with partners over there to promote the route."
In total, more than 300 onward connections are available via Newark.