At the age of 34, Fehn gained international recognition for his design of the Norwegian Pavilion at the 1958 Brussels World Exhibition. 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). Other notable works include the Norwegian Glacier Museum at Fjærland (1991-2002) and the National Museum of Art, Architecture and Design in Oslo (2003–08).