The first stage will begin on Noirmoutier-en-l'lle on 30 June and cross the Passage du Gois, a causeway which is often flooded.
The 2011 edition, which was won by Australia's Cadel Evans, also began on the island and crossed the passage.
Dusseldorf will host the 2017 Grand Depart on 1 July after London turned down the chance to hold the event.
The 2018 Tour de France Grand Depart will take place in Vendee in western France.