Kingston, 33, is contracted to appear in at least 22 episodes and has an "open-ended" arrangement after that, her agent said yesterday. There are no details of her role yet, but her first episodes are due to air this autumn.
"Her character hasn't even got a name yet," her agent said.
Fans will be feverishly speculating which of ER's regulars could be destined to fall under Kingston's sensual spell - George Clooney's womanising Dr Doug Ross, vulnerable divorcee Dr Mark Green or perhaps the boyish Dr Carter.
The hospital series, made by Warner Brothers Television, is avidly followed by millions across America and is also one of Channel 4's biggest successes.
It will make Kingston one of Britain's highest profile acting exports, on a par with her estranged husband, Ralph Fiennes, the star of the Oscar- winning movie The English Patient.
It also means she will be swapping the couple's former flat in Peckham, south London, for a Hollywood home during the hectic shooting of the series - filming 22 hour-long episodes in a year is considered the norm in the US.
Another British thespian export, Kenneth Branagh, has also landed a key part in the US, as the lead in the next Woody Allen film.
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