The death of Jean-Jacques Savin was announced by his friends on a Facebook page that had been chronicling his voyage.
They had received no news since Friday, after he activated two distress beacons the previous night indicating he was in "great difficulty", his friends told AFP on Saturday.
In the later Facebook post they said maritime rescue services located his body on Saturday inside the cabin of his boat, named “Audacious", which was found overturned off the Azores Islands, a mid-Atlantic Portuguese archipelago.
The precise circumstances of the tragedy were unknown, Savin's friends added.
The former soldier set off on January 1 from the southern tip of Portugal on the westward voyage he had anticipated would take about three months.
In 2019, Savin — from the Gironde department in southwest France — had previously floated alone across the Atlantic in a large barrel-shaped capsule. Propelled only by winds and currents, that crossing from Spain’s Canary Islands to the Caribbean took 127 days.
“Unfortunately, the ocean this time was stronger this time than our friend, he who so loved navigating and the sea," the Facebook post announcing his death said.
His journey this time had not gone to plan, blown off course by bad winds which meant the trip would be extended by some 900 kilometres. Upon his last contact he was located north of Madeira, heading for Ponta Delgada in the Azores.
Last Wednesday he posted on Facebook that he was experiencing a strong swell and winds, which was "costing me physical energy". But, he added, "I am not in danger!"
Jean-Jacques Savin had spoken of wanting to become the "doyen of the Atlantic" as "a way of mocking old age".
A former paratrooper, pilot and national park keeper in Africa, Savin turned 75 earlier this month on board his two-cabin, eight-metre long rowing boat — and had packed champagne and foie gras to celebrate.
"I'm heading for the open sea, I'm taking three months holiday," he joked.
"He was an extraordinary, atypical man," said Xavier Daney, mayor of Arès in Arcachon Bay where Savin lived, describing the rower as an "exceptional adventurer". The mayor added that his thoughts were with Savin's "daughter Manon, partner Jackie and the whole team of volunteers".