He was born in Oslo as a son of barrister and director Bernt Bjelke Lund (1898–1956) and Irlin Sommerfelt (1902–1974).
In 1978 he started a private lawyer's firm, with among others the Norwegian Non-Fiction Writers' and Translators’ Association as a client.
From 1994 to 1996 he chaired the Lund commission, which looked into illegal political surveillance in Norway in the post–World War II period.
Andenæs, one of the most prominent former professors of law in Norway, and the Criminal Justice Commission of 2002.
[4] He has been a critical voice in the human rights field, particularly about issues regarding surveillance and coercive psychiatric care.