"Emmanuel Macron nominated the three volunteer members of the National Society for Rescue at Sea (SNSM) for the Legion of Honour award," the French presidency said in a statement.
Four other occupants of the lifeboat who capsized in bad weather were injured.
"This tragedy recalls the risks taken, the commitment granted by the 8,000 sea rescuers in our country,” the statement reads
"In late morning, a boat from the SNSM capsized 800 metres from the coast around Les Sables d'Olonne with seven people on board," the local prosecutor's office said in a statement.
Three of them died while four managed to swim to shore, the statement added.
Ces hommes sont des héros. J’ai décidé de les nommer, à titre posthume, chevalier dans l’ordre national de la Légion d’honneur. https://t.co/YMHpKjG7RpEmmanuel Macron (@EmmanuelMacron) June 8, 2019
"These tragic deaths have sparked deep emotions within the ocean rescue services," said SNSM chief, Xavier de la Gorce.
The team from the National Society of Sea Rescue (SNSM) had been attempting to help a fishing boat which was struggling in the giant swell caused by storm Miguel, which packed winds of up to 120 kilometres an hour (75 mph).
Maritime officials said the crew was using one of the SNSM's "all weather" vessels, specially designed to be unsinkable and to automatically right itself if capsized.
Photos taken before the accident show waves crashing over the front of the small boat as it headed out.
After capsizing, it ended up upside down on the rocky shore.
The captain of the fishing boat is also missing, and officials said he probably had crew members on board as well.
"So far we haven't been able to find the fishing boat. We've found fragments of the boat and an empty lifeboat," the regional maritime authority told AFP.
It said the rough sea conditions were at level five of the nine on the Douglas scale, indicating waves of up to four metres (13 feet) high.
Yannick Moreau, the mayor of Les Sables d'Olonne, said it was "incomprehensible that any boat went out on a day like today."
The SNSM gets funding from the state but is a nonprofit organisation run by around 8,000 volunteers.
"The SNSM boat at Les Sables is a crew of professionals, sailors who know the ocean, know the conditions," Moreau said, adding that his town was "in shock."
Storm Miguel has led the French weather service to put large areas of the Atlantic coast on alert for high winds and heavy rain.