Plouharnel is a seaside town located in the south of Morbihan, 12 km (7.5 mi) southwest of Auray, 25 km (16 mi) southeast of Lorient and 27 km (17 mi) west of Vannes. 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.