Lannach is a municipality in the district of Deutschlandsberg, in the Austrian state of Styria. It lies in the southern part of Styria, within the broader region known as West Styria, and forms part of the administrative district whose seat is the town of Deutschlandsberg.
As a municipality, Lannach is one of the constituent local administrative units of the Deutschlandsberg district, a district that covers the western and southwestern portions of Styria. The area around Lannach is part of the rolling hill country and valley landscapes characteristic of this part of Austria, situated within the eastern Alpine foreland.
Lannach is located in Austria's southern federal state of Styria, whose capital is Graz. The municipality shares the district of Deutschlandsberg with a number of other communities, and its position places it within the West Styria sub-region of the state.