Peggau is a municipality in the district of Graz-Umgebung, in the Austrian state of Styria. It lies in the central part of the state, within the wider Graz metropolitan area, north of the city of Graz.
The municipality is situated in the valley of the Mur river, at the point where the river cuts through the mountains of the Grazer Bergland. This setting gives Peggau its best-known natural feature, the Lurgrotte, a large karst cave system whose entrance lies in the municipality; part of the cave is open to visitors.
Peggau is connected to Graz and the surrounding region by road and by the railway line running through the Mur valley, and it functions largely as a residential and commuter community within the Graz-Umgebung district.