Bad Sankt Leonhard im Lavanttal (Slovene: Sveti Lenart v Labotu) is a spa town in the district of Wolfsberg in the Austrian state of Carinthia.

The municipal area comprises the cadastral communities of Erzberg, Görlitzen, Kliening, Bad Sankt Leonhard proper, Schiefling, Schönberg, Theißing, and Twimberg.

The area was settled since ancient times, when a Roman road led through the Lavanttal up to the Obdach Saddle pass and the Mur valley in present-day Upper Styria.

The settlement below the chapel was first mentioned in a 1278 deed, its citizens already had received town privileges by 1311, at the time when the Gothic parish church was erected.

During the Great Depression in the 1930s, several medieval stained glass windows of the parish church were sold and are now on display at The Cloisters museum in New York City.