Mellac (French pronunciation: [mɛlak]; Breton: Mellag) is a commune in the Finistère department of Brittany in north-western France.

The village centre is located 4.5 km (2.8 mi) northeast of Quimperlé.

The river Isole forms the commune's northern and eastern borders.

Mellac is border by Saint-Thurien and Querrien to the north, by Tréméven to the east, by Quimperlé and Baye to the south and by Le Trévoux and Bannalec to the west.

The oldest surviving parish registers date back to 1562.