Rene Marratier hid the risks to La Faute-sur-Mer to avoid putting off property developers, the court said.
The storm Xynthia hit western Europe in early 2010. The storm knocked down seawalls in La Faute-sur-Mer, leading to severe flooding.
Marratier called the verdict "unjust" and said he would appeal.
On Friday, the court said that Marratier knew La Faute-sur-Mer, a west coast resort in the Pays de la Loire region, was at risk of flooding.
However, he "deliberately hid" the risk so that he could benefit from the "cash-cow" of property development, the court added.
Marratier's deputy was jailed for two years.
Xynthia swept through Spain, Portugal and France in February 2010, killing at least 50 people in western Europe.
