[2] In 1949, Fehn and architect Geir Grung (1926–1989) won the competition for the Museum Building for the Sandvig Collections at Maihaugen in Lillehammer.

Later he moved to Paris, where he worked for two years in the studio of Jean Prouvé, and where he knew Le Corbusier.

[3] At the age of 34, Fehn gained international recognition for his design of the Norwegian Pavilion at the 1958 Brussels World Exhibition.

[2] In the 1960s he produced two works that have remained highlights in his career: the Nordic Pavilion at the Venice Biennale (1962) and the Hedmark Museum in Hamar (1967–79).

He also lectured in the United States at the Cranbrook Academy of Art in Bloomfield Hills, Michigan, Cooper Union in New York City and Massachusetts Institute of Technology in Boston.

[7] [8] His highest international honour came in 1997, when he was awarded both the Pritzker Architecture Prize and the Heinrich Tessenow Gold Medal (Heinrich-Tessenow-Medaille).