Authorities were called in to assist more than 2,300 people after rivers overran their banks and streets and homes were flooded, with some residents having to be rescued with helicopters.
Local authorities said on Sunday that an elderly couple had died in the town of Bagnols-en-Foret in the south-western Var region from carbon monoxide poisoning while trying to use a motorised pump to empty their flooded basement.
A 51-year-old German homeless man was also found dead Saturday after he was washed away in floodwaters in the southern Herault region.
In Var, one of the worst-hit regions, more than 1,600 people were evacuated or assisted by authorities and about 3,900 homes were without electricity.
In the Alpes-Maritimes region, 700 people had been evacuated since Saturday morning, authorities said.