He graduated from the Oslo School of Architecture in 1949 in Oslo, Norway.
He was a founding member of the Progressive Artists Group Oslo Norway, the Norwegian branch of the International Congress of Modern Architecture.
He established his own architectural practice in Norway in 1954.
He was a professor of architecture at the Oslo School of Architecture and Design from 1971 until 1995.
He was awarded the Pritzker Prize after completing 11 buildings including the Hedmark Museum (1973) in Hamar, and the Aukrust Museum (1993-1996) in Alvdal, dedicated to the painter Kjel Aukrust.
He designed the Oslo headquarters of the Gyllendal publishing house in 2007 and the Norwegian Museum of Architecture in March 2008.
He is survived by his son, Guy Fehn, of Denmark and four grandchildren including Jacob Fehn.
He also built the Nordic Pavilion at the 1962 Venice Biennale and the Glacier Museum at Fjaer Fjord in Norway.
Norwegian architect who won the Pritzker Architecture Prize in 1997.