Bryhn studied law at the Royal Frederick University from 1925, graduating in 1930. While being a student he was a member of the socialist and pacifist organization Clarté. From 1930 he worked in Svolvær for two years, and later with the police in Oslo. After the German occupation of Norway, Bryhn served as assistant of Chief of Police of Oslo Kristian Welhaven. When Welhaven was removed from his position, Bryhn and others started undercover intelligence work within the police corps. He was dismissed from the police in December 1941. From 1942 he became a leader of the police group of the undercover resistance group 2A, and cooperated closely with Asbjørn Sunde. He fled to Sweden, where he built up surveillance and security service at Norwegian legation in Stockholm. His main task was to control refugees and couriers from Norway, and he eventually became a controversial person at the legation.
He was assistant secretary (Norwegian: byråsjef) at the Ministry of Justice in the Norwegian exile government in London from 1943 to 1945. When the war ended in 1945 he became leader of the department which was responsible for the investigation of German criminals of war in Norway. From 1945 to 1957 he was a police inspector in Oslo. From 1957 to 1966 he was head of the Police Surveillance Agency (Norwegian: Politiets Overvåkningstjeneste, POT). After a controversy with leader of the Norwegian Intelligence Service Vilhelm Evang, when Bryhn arrested Evang's secretary and charged her for espionage for the Soviet Union, both Bryhn and Evang had to leave their positions. After Bryhn had left the service, Gunnar Haarstad became the next head of POT. Bryhn was Chief of Police of Bergen from 1967 to 1976.
- Andersen, Roy. "Asbjørn Bryhn". In Helle, Knut. Norsk biografisk leksikon (in Norwegian). Oslo: Kunnskapsforlaget. Retrieved 31 January 2010.
- Borgersrud, Lars (1995). "Bryhn, Asbjørn". In Dahl, Hjeltnes, Nøkleby, Ringdal, Sørensen. Norsk krigsleksikon 1940-45 (in Norwegian). Oslo: Cappelen. p. 55. ISBN 82-02-14138-9. Retrieved 31 January 2010.
- Henriksen, Petter (ed.). "Asbjørn Johan Bryhn". Store norske leksikon (in Norwegian). Oslo: Kunnskapsforlaget. Retrieved 31 January 2010.
- Eriksen, Knut Einar. "Gunnar Haarstad". In Helle, Knut. Norsk biografisk leksikon (in Norwegian). Oslo: Kunnskapsforlaget. Retrieved 1 February 2010.
||Director of the Norwegian Police Surveillance Agency