He was born in Moss as a son of dentist Arne Arnesen (1900–1975) and modist Dordi Texnæs (1906–1996).
Arnesen finished his secondary education, lived in Hamar for some time before enrolling in political science at the University of Oslo in 1949.
[1] He was stationed at the United Nations from 1957 to 1960, worked out of Norway with development aid until 1964, then two years at the embassy in Morocco.
Back in Norway he was an assistant secretary in the Ministry of Foreign Affairs from 1966 to 1971, then leader of the minister's secretariat.
After a short stint in the newspaper Arbeiderbladet in 1973 he served as State Secretary in the Ministry of Foreign Affairs from 1973 to 1975.