Øystein Thommessen was a Norwegian lawyer.

He was born in Kristiania

Oslo

Oslo is a municipality, as well as the capital and most populous city in Norway. As a municipality , it was established on 1 January 1838. Founded around 1048 by King Harald III of Norway, the city was largely destroyed by fire in 1624. The city was moved under the reign of Denmark–Norway's King...

 as a son of Jakob Peter Thommessen and Maja Johannessen. He was a nephew of Ola Thommessen

Ola Thommessen

Ola Thommessen was a Norwegian newspaper editor. He was the long-time editor of Verdens Gang and Tidens Tegn.-Early and personal life:...

 and a first cousin of Rolf Thommessen

Rolf Thommessen

Rolf Thommessen was a Norwegian journalist, newspaper editor and politician. He edited the newspaper Tidens Tegn from 1917 to 1938...

. In April 1924 in Kristiania he married Ebba Lindeman.

He took his examen artium

Examen artium

Examen artium was the name of the academic certification conferred in Denmark and Norway, qualifying the student for admission to university studies. Examen artium was originally introduced as the entrance exam of the University of Copenhagen in 1630...

 at Aars og Voss skole in 1908, and then graduated from the Royal Frederick University

University of Oslo

The University of Oslo , formerly The Royal Frederick University , is the oldest and largest university in Norway, situated in the Norwegian capital of Oslo. The university was founded in 1811 and was modelled after the recently established University of Berlin...

 with the cand.jur. degree in 1912. He was a deputy judge in Aker

Aker, Norway

Aker is a former municipality in Akershus, which lends its name to a municipality and a county in Norway. The name originally belonged to a farm which was located near the current Old Aker Church...

 from 1913 to 1916 and a junior solicitor from 1916, until taking the lawyer's credentials in 1919. From 1922 he worked as a law firm partner. His specialties were patent law, trademark law and tax law

Tax law

Tax law is the codified system of laws that describes government levies on economic transactions, commonly called taxes.-Major issues:Primary taxation issues facing the governments world over include;* taxes on income and wealth...

, and he wrote a seminal article on tax law in Norsk Retstidende

Norsk Retstidende

Norsk Retstidende is a periodical published by the Norwegian Bar Association. The journal was established in 1836, and had its current name since 1909. Norsk Retstidende publishes judgements of the Supreme Court of Norway, and rulings of the Appeals Selection Committee....

in 1934, and a commentary on trademark law in 1961.

Between 1940 and 1945 he was a member of the Norwegian resistance movement

Norwegian resistance movement

The Norwegian resistance to the occupation of Norway by Nazi Germany began after Operation Weserübung in 1940 and ended in 1945. It took several forms:...

. He was a member of the leading inner circle Kretsen from 1943, later Hjemmefrontens Ledelse. In cooperation with Tor Skjønsberg

Tor Skjønsberg

Tor Vangen Skjønsberg was a Norwegian resistance leader, by education he was a lawyer.In 1941 Tor Skjønsberg called for a meeting "Grimelundsmøtet" which is considered the start of organized resistance in Norway....

 he had regular contact with the Norwegian legation in Stockholm

Norwegian legation in Stockholm

The Norwegian Legation in Stockholm played a significant role during the Second World War. Until 9 April 1940 the legation consisted of four persons, and at the end of the war about 1,100 persons were connected to the legation. Refugee cases were among the legation's most central tasks...

, securing several monetary loans through contacts with the government-in-exile representatives stationed in Stockholm. He worked there himself from 1944, after he had to flee Norway. He was later a Norwegian delegate to the United Nations Conference on International Organization

United Nations Conference on International Organization

The United Nations Conference on International Organization was a convention of delegates from 50 Allied nations that took place from 25 April 1945 to 26 June 1945 in San Francisco, California. At this convention, the delegates reviewed and rewrote the Dumbarton Oaks agreements...

 in 1945 and the Paris Peace Conference of 1946.

He was chairman of the Norwegian Museum of Cultural History from 1948 to 1966, and a board member of Gyldendal Norsk Forlag

Gyldendal Norsk Forlag

Gyldendal Norsk Forlag, commonly referred to as Gyldendal, is one of the largest Norwegian publishing houses .-Gyldendal Norsk Forlag AS:Gyldendal Norsk Forlag AS was founded in 1925...

 from 1941 to 1965, Elektrokemisk

Elkem

Elkem is one of Norway's largest industrial companies, and one of the world's leading suppliers of metals and materials. The company's main products are aluminium, energy and silicon as well as specialised products such as ferrosilicon to foundries, microsilica and carbon...

 from 1952 to 1965 and Orkla Grube-Aktiebolag

Orkla Group

Orkla Group is a Norwegian industrial conglomerate operating in the Nordic region, Eastern Europe, Asia and the US. The company's main divisions are branded consumer goods, aluminium solutions, materials, associates and financial investments.-Operations:...

 from 1956 to 1957. He was also a vice chancellor of the Order Council. He died in 1986.