She was born in Christiania, a daughter of Peter Elias Bjørnson and Laura Marie Mathilde Riiser Larsen, and niece of Bjørnstjerne Bjørnson.

She was married first to painter Eyolf Soot, later to actor Harald Stormoen.

She is the mother of Botten Soot and Guri Stormoen.

The theatre opened with Margrethe Munthe's play Askepott, and continued with other stage adaptations of fairytales and children's books.

Among her books are Dundor-Heikka from 1916, Våre barnesanger from 1926, and 30 år med barneteatret from 1950.