Eric Vannier, 60, was also given a six-month suspended sentence, France 24 reported Wednesday.
He had been sued by his mayoral predecessor, Patrick Gaulois, 60, for positioning a bus stop in such a place that the Normandy island's 3 million annual visitors would pass by Vannier's shops and restaurants.
Vannier owns about 80 percent of the businesses on the rocky island and 20 percent on the adjoining coast. Gaulois owns three restaurants and a sandwich shop on the mount, making him Vannier's biggest competitor.
Gaulois filed a complaint after the local tourist board closed a parking lot at the foot of the island in 2012 and built 4,000 parking spaces on the mainland. A shuttle service was created to carry tourists to Mont Saint-Michel but the bus stop was placed about a half mile away. Visitors to the world heritage site had to walk past businesses owned by Vannier to get to the bus stop.
Vannier has been mayor of Mont Saint-Michel since 1983, except for a period between 2001 and 2008 when Gaulois was mayor.