The 30-year-old man reportedly tried to swim across the Caen Canal near Pegasus Bridge – a famous Second World War landmark – late on Saturday night.
He was in France supporting D-Day commemorations, the Ministry of Defence told Sky News, and was swimming during time off.
He was stationed at Ranville on the Normandy coast with several thousand other British soldiers, French media said.
Local police are investigating and are not looking for anyone else.
The MoD said in a statement: “It is with sadness that we must confirm the death of a service person in France. Our thoughts are with their family at this difficult time.”
The taking of Pegasus Bridge was a major objective following the Normandy landings on 6 June 1944 – also known as D-Day.
Holding both it and nearby Ranville Bridge helped limit the effectiveness of a German counter-attack.
