Sankt Margarethen im Lungau is a municipality in the district of Tamsweg, in the state of Salzburg, Austria. It lies in the Lungau, the southeastern region of Salzburg, and is one of the smaller communities within the Tamsweg district.
The municipality is located in a mountainous alpine area of central Austria. Its name distinguishes it from other places named Sankt Margarethen, and the "im Lungau" suffix refers to its position within the Lungau region.