Outside of politics, he graduated with the cand.philol. degree in 1909, and spent his professional career as a journalist and a state archivist. He was a journalist in Socialdemokraten from 1909 to 1912, Ny Tid from 1915 to 1917, Arbeiderbladet from 1917 to 1924 and Norges Kommunistblad from 1928 to 1929. He was also editor-in-chief of Rjukan Arbeiderblad from 1925 to 1928 and the working class encyclopedia Arbeidernes Leksikon from 1930 to 1936. As a state archivist he worked in the National Archives (Riksarkivet) from 1912 to 1915, followed by the regional state archives: in Trondhjem 1915-1917, Kristiania 1917-1922 and Kristiansand 1934-1953.
On the local level Friis was a member of Aker municipal council between 1919 and 1922, and of Kristiansand city council between 1937 and 1940. He chaired the municipal party chapter from 1936 to 1937.
Friis represented the Labour Party at the Second and Third Comintern World Congresses; he was also a member of the Executive Committee of the Communist International from 1920 to 1921. In 1923, Friis supported Martin Tranmæl and withdrawal of the Labour Party from the Comintern. This saw the Communist Party break away from the Labour Party. However, Friis became a Communist Party member in 1928. He left the party in 1933, and rejoined Labour in 1936. Friis opposed the asylum for Leon Trotsky to come to Norway in 1935 and campaigned against the former Bolshevik leader when he lived in Oslo.
After World War II Friis was elected to the Parliament of Norway from the Market towns of Vest-Agder and Rogaland counties in 1945, and was re-elected on one occasion. He was still to be found on the left wing of the Labour Party, and was among the founders of the newspaper Orientering in 1953, having published the book Kritikk av norsk utenrikspolitikk etter krigen in 1952. He was one of its chief editors until his death in 1956.