He was born in Vestre Toten, a son of farmers Petter Hansen Gaarder and Kari Alfstad. He graduated as cand.jur. in 1924, and later served as judge, secretary at the Ministry of Justice, and lecturer at the Norwegian School of Economics. He was appointed Justice of the Supreme Court of Norway from 1946. He was decorated Commander of the Order of St. Olav in 1964.
