LONDON — The Japanese carmaker Nissan, one of Britain’s largest overseas employers, announced on Thursday that it would build a new car at its existing plant in Sunderland, giving Prime Minister Theresa May of Britain a considerable political gift.

Sunderland has been a symbolic flash point in Britain’s decision to leave European Union.

In the run-up to the vote, Nissan had threatened to stop investing in the plant, creating the potential for thousands of job losses in the area. But the economic uncertainty did not dissuade the residents of Sunderland from voting overwhelmingly to exit.

The Nissan deal will be closely dissected for early indications about how Ms. May will potentially navigate the thorny negotiations with major industries. Nissan acted after getting reassurances from Mrs. May that the company would be protected from any negative economic impact from the so-called Brexit.

Mrs. May called the announcement “fantastic news for the U.K.,” saying that Nissan was “at the heart of this country’s strong automotive industry,” which is almost entirely foreign-owned and ships more than half its exports to the European Union.