When the Communist Party split from Labour in 1923, Jullum was hired in their main newspaper "Norges Kommunistblad" where he stayed until 1926. In 1927 he rejoined the Labour Party. He was hired as editor-in-chief of "Tidens Krav". From 1928 to 1964 he worked in "Arbeiderbladet". He was acting editor for five months in 1940. In April 1940, Norway was invaded by Germany. Jullum was acting editor until September 1940, when the newspaper was shut down for the remainder of World War II. He was also a board member of the Norwegian Press Association from 1930 to 1936.