Briton Nick Thomas, 45, set out from Dover on Saturday morning and had reportedly been in the water for some 16 hours when he got into difficulty.
He was pulled from the sea in an unconscious state and rescuers administered CPR before he was transferred to hospital in Calais, France. But sadly, he was pronounced dead a short time later.
It is understood that he was less than a mile from the finishing point when tragedy struck.
Mr. Thomas had previously managed to swim all the way from England to France in 2014.