"We can confirm that a U.K. military healthcare worker in Sierra Leone has tested positive for Ebola," said a PHE spokesman.
He added that medical experts were making sure appropriate care was being delivered.
A decision on whether the individual will be evacuated to Britain for treatment has not yet been made.
"Any individuals identified as having had close contact will be assessed and a clinical decision made regarding bringing them to the U.K.," said the spokesman.
The worker, who is reportedly a female, is the third British citizen to test positive for Ebola since the epidemic broke out in West Africa.
Between 600 and 700 British servicemen and women are reportedly working in Sierra Leone to help fight Ebola. More than 9,800 people have died from Ebola in the current outbreak, according to the World Health Organization (WHO).
By Ruchi Singh