The man and woman were discovered dead last night by neighbors coming for dinner at their second home in Gignac, Hérault, in the south of France.
The cause of death is currently unknown and an investigation has been opened by the local police.
Their neighbours who were meant to be coming round for dinner with the English couple raised the alarm, French media reported.
When noone answered the door, they entered the property to discover the bodies of couple, who are in their eighties, floating in the pool.
Despite the efforts of the emergency services, they could not be saved.
An autopsy will determine the cause and time of death, but there were no signs of a break-in or theft in the house.
Although nothing has been ruled out, investigators indicate an accident is most likely at the present time.
A source told news outlet La Dépêche: “It is not ruled out that one of the spouses witnessed the drowning of the other then came to their aid and sank themselves.”
The British couple regularly spent their holidays at the “opulent” property.
The local mayor who knew them described both as: “very nice people who came many times a year and who occasionally participated in the town’s activities”.