Anne Marie Andersen was born in Elverum, Norway, to an affluent family. She trained as a teacher and taught for several years before turning to a career in the theater. She toured Norway as an actress and was admitted to the National Theatre. In 1909, she married the writer Knut Hamsun, with whom she had four children. She also became a writer under the name Marie Hamsun, publishing her first collection of poems in 1922. She went on to write short stories and poetry aimed at a young audience. She also published two autobiographical works, Regnbuen (The Rainbow, 1953) and Under gullregnen (1959). She supported the Third Reich and the German Occupation of Norway during World War II and was a member of Vidkun Quisling's Nazi Party. In 1947, she was convicted of treason, but received amnesty and was released after spending nine months in prison.