Doctors Without Borders, known by its French acronym MSF, said a female volunteer had contracted the killer virus while on assignment in Liberia.
France's health ministry said she "will be repatriated to Paris in conditions of maximum security in a dedicated air ambulance".
The Ebola outbreak in west Africa is the worst in history, with more than 2,400 people already dead and quickening infection rates threatening to spiral out of control.
The World Bank on Wednesday warned that fear of the deadly virus is choking off economic activity in the worst-hit countries, with potentially "catastrophic" results.
MSF has played a major role in combatting the epidemic, with more than 2,000 staff members in the region including some 200 international workers.
But health bodies have warned that medical facilities are already so overwhelmed by new cases that they are having to turn people away to die on the streets.
MSF president Mego Terzian said the French Ebola patient, said to be in stable condition, was expected back in Paris on Thursday.
She is the first Western MSF worker to have caught the disease, though "unfortunately several African MSF colleagues have been affected," he added.
MSF gave no further details on the woman involved whom, they said, had been placed in isolation on Tuesday after showing symptoms of the deadly disease.- 'Spiralling out of control' -
The United Nations Security Council is to hold an emergency session on Thursday to discuss ramping up the global aid response to the crisis.
US President Barack Obama on Tuesday pledged to send 3,000 military personnel to west Africa to combat the epidemic, "the likes that we have not seen before".
"It's spiralling out of control. It is getting worse. It's spreading faster and exponentially," he said.
President Obama's announcement "is a significant moment in the battle against Ebola," Liberian President Ellen Johnson Sirleaf said in a statement.
"Our American partners realise Liberia cannot defeat Ebola alone," said Sirleaf, whose country has registered more than half of the reported deaths from the disease.
"We hope this decision by the United States will spur the rest of the international community into action."- 'Catastrophic blow' -
The current epidemic, the worst since Ebola was discovered in the Democratic Republic of Congo in 1976, has killed more than half of those infected.
The virus can fell its victims within days, causing severe fever and muscle pain, weakness, vomiting and diarrhoea -- in some cases shutting down organs and causing unstoppable bleeding.
No licenced vaccine or treatment exists, although experts have stepped up their research in response to the crisis.
On Wednesday, a healthy British volunteer became the first to receive a new vaccine for the Ebola virus in a trial at the University of Oxford.
The volunteer is one of 60 who will receive the drug in tests that will run alongside similar trials in the US in the hope of producing a vaccine by the end of the year.
The vaccine specifically targets the Zaire variety of Ebola, which has killed 2,461 people out of 4,985 recorded cases in Guinea, Liberia, Sierra Leone, Nigeria and Senegal since the start of the year, according to the World Health Organization.
But on Wednesday, the World Bank warned that even the fear of the disease is strangling the economies of the worst-hit countries, keeping workers at home and placing a heavy burden on their strained health systems.
If it spreads unchecked across Guinea, Liberia, and Sierra Leone, the bank predicted its impact could grow eight-fold, "dealing a potentially catastrophic blow to the already fragile states".
"The sooner we get an adequate containment response and decrease the level of fear and uncertainty, the faster we can blunt Ebola's economic impact," said World Bank President Jim Yong Kim.
In the worst-case scenario, Liberia's economic growth could fall by 11.7 percentage points next year, plunging the country into recession with a 4.9 percent contraction.
In Sierra Leone, the worst-case impact could be 8.9 percentage points lost from growth in 2015, and in Guinea, 2.3 points.
Sierra Leone is preparing for a nationwide three-day lockdown in an attempt to curb the spread of the disease.
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