The commune is bordered by Atlantic Ocean except to the north and the east.

The northern part of the isthmus connecting the mainland to the ancient island of Quiberon is located in the commune's southern part.

At Auray station connections to Paris and other places in France are offered.

Inhabitants of Plouharnel are called in French Plouharnelais.

The commune contains a number of megalithic monuments including those at Le Vieux-Moulin, comprising six stones weighing up to ten tons.