Background
He was born in Kviteseid, a son of Didrik Cappelen, and a brother of Hans Cappelen. During the occupation of Norway by Nazi Germany Cappelen worked together with his father, Carl P. Wright and Sverre Løberg in organizing resistance activities in the county of Telemark, Norway.
Career
Cappelen was arrested and in prison from 1940 to 1942 in Oslo, but escaped 30 January 1942. Cappelen was appointed at the Norwegian Legation in Stockholm from 1942, and then at the Norwegian Ministry of Justice in exile in London. He served as prosecutor in Skien from 1946-1956 and as county judge from 1956 to 1970.
He was elected as suppleant to the Parliament of Norway several times, and replaced Sveinung O. Flaaten after his death in 1962.