He was born in
Trondheim, the son of director Christian Fredy Michael Jahn (1837–1914) and Elisabeth Wilhelmine Wexelsen (1853–1930). He was a grandson of
Vilhelm Andreas Wexelsen, a grandnephew of
Marie Wexelsen and a first cousin of
Per Kvist. He
finished his secondary education at
Trondheim Cathedral School in 1902 graduated from the
Royal Frederick University with the
cand.jur. degree in 1907. He worked as a deputy judge in
Lofoten before enrolling at the university again; he graduated in economics in 1909. He was hired in
Statistics Norway in 1910. In April 1911 he married
Martha Larsen Jahn. From 1913 he was a teacher at
Kristiania Commerce School and the university, jobs he left in 1918 and 1920 respectively. From 1917 to 1919 he worked in
Rasjoneringsdirektoratet, and from 1919 to 1920 he was the director there. In 1920 he became director of Statistics Norway. He was a member of the
Norwegian Academy of Science and Letters from 1927. From November 1934 to March 1935 he was the
Minister of Finance and Customs in
Mowinckel's Third Cabinet. He became a member of the
Norwegian Nobel Committee in 1937, In 1940 he was a member of the
Administrative Council, which tried to maintain Norwegian political governance despite the
German invasion and
occupation of Norway. He marked himself as a strong proponent of
resistance to Germany, and was a member of the central leadership of the resistance: "
Kretsen" and
Hjemmefrontens Ledelse. After the German surrender, he saw himself as a candidate to become Prime Minister of Norway, but Hjemmefrontens Ledelse chose
Paal Berg as their candidate. He instead became Minister of Finance and Customs of the Norwegian interim government,
Gerhardsen's First Cabinet, on 25 June. He remained so until 4 November the same year, and also served on the Board of Governors in the
International Bank for Reconstruction and Development and the
International Monetary Fund in 1945. He then headed the
Central Bank of Norway from 1946 to 1954. He presided over the
International Statistical Institute from 1947 to 1951, and was an honorary member. As the Chairman of the Nobel Committee, he delivered the Presentation Speech to The Nobel Peace Prize 1947 to the Quaker Friends Service Council (British) and American Friends Service Committee (http://www.nobelprize.org/nobel_prizes/peace/laureates/1947/press.html). He was also a member of the Liberal Party's national board for some time. He died in January 1971 in Oslo. ==U Thant controversy==