The river originates in the small Lake Lavant (Lavantsee) at the southern slope of the Zirbitzkogel mountain in Styria, at a height of . It then runs southeastwards and after reaches the border with Carinthia. The river flows down the Lavanttal with the towns of Bad Sankt Leonhard, Wolfsberg and Sankt Andrä, until it reaches the Drava shortly before it crosses the border to Slovenia.