The States of Jersey Police said that that a local fisherman recovered the body from the water.
The deceased individual was wearing a wetsuit and diving gear.
The RNLI’s St Helier all-weather lifeboat, which was conducting an exercise at sea, responded immediately to the call.
Upon arrival, the RNLI crew transferred the body onto their lifeboat in order to bring the body safely onshore to Jersey.
The States of Jersey Police were requested on the scene, and the Jersey Lifeboat Association transported officers to the location.
In a statement, police said: “We are now working in close cooperation with our French counterparts to conduct a thorough investigation to ascertain the circumstances surrounding this incident.”
The French coastguard confirmed that a diver had been missing from the north coast of Brittany for a week, since Monday 25 March.
The identity of the deceased is subject to confirmation, and the next of kin will be notified accordingly.
The States police sent their thoughts to the family and friends of the victim.