The individual is likely to have been exposed to the virus but has not been diagnosed with Ebola and does not have symptoms.
Public Health England said the individual has been admitted to the Royal Free Hospital in London for assessment and next of kin have been informed.
Professor Paul Cosford, PHE's director for health protection and medical director, said: "Our thoughts are with this person,
who has been courageous in helping those affected in West Africa, and in preventing the wider spread of Ebola.
"We have strict, well-tested protocols in place for this eventuality and we are confident that all appropriate actions have been taken to support the healthcare worker concerned and to protect the health of other people."
- Needle-stick injuries involve a piercing of the skin, typically by a needle point but also by other sharp instruments or objects.
- They are a serious occupational hazard for doctors, healthcare workers and those working in law enforcement.
- The injuries are of particular concern because of the risk of blood-borne diseases being transmitted.
PHE said the individual had arrived back in the UK today on an RAF flight after being exposed to the virus in a "frontline care setting".
The patient will be monitored for the remainder of their 21-day incubation period. Decisions on immediate and ongoing care will be made by the clinical team at the Royal Free Hospital.
It is believed that the medic would have been working at the Kerry Town treatment centre and that the injury would have happened within the last 48 hours.
This is the period when someone who has had a known exposure to Ebola would have had a window of opportunity to be safely transported to the UK as they are not yet contagious.
It is believed the military transport, bringing the patient back as a precautionary measure, arrived at RAF Brize Norton in Oxfordshire in the early hours of this morning.
The Kerry Town complex includes an 80-bed treatment centre to be managed by Save the Children and a 12-bed centre staffed by British Army medics specifically for health care workers and international staff responding to the Ebola crisis.
The patient is being treated at London's Royal Free Hospital, where British nurses Pauline Cafferkey and Will Pooley were treated in a specialist isolation unit. They were each diagnosed with the disease after helping treat patients in Africa.
A statement from the Royal Free Hospital said: "We can confirm that a UK military healthcare worker has been admitted to the Royal Free Hospital today following a needlestick injury while treating a person with Ebola in Sierra Leone.
"The individual has been admitted to the Royal Free Hospital for assessment. The individual is likely to have been exposed to the Ebola virus but has not been diagnosed with Ebola and does not have symptoms."
Cafferkey, 39, from Cambuslang, in South Lanarkshire, was discharged from the RFH this week after making a full recovery from Ebola. Cafferkey, who had volunteered with Save the Children at a treatment centre in Kerry Town, in Sierra Leone, was diagnosed with Ebola on December 29, after returning to Glasgow via London.
William Pooley, 29, who contracted Ebola while volunteering in West Africa, has returned to Sierra Leone to resume his work after recovering from the virus.
The nurse, from Eyke in Suffolk, was flown back to the UK by the RAF on August 24 and was taken to the RFH.