In 1930, he was hired as a research fellow at the Royal Frederick University, and earned the dr.juris degree already in 1931, with the thesis Betingelsene for testamenters gyldighet efter norsk rett.
When the Nazi authorities attempted to change the rules for admission to the university in autumn 1943, a protest ensued.
[2] The staff members, including Johannes Andenæs, Eiliv Skard, Johan Christian Schreiner, Harald Krabbe Schjelderup, Anatol Heintz, Odd Hassel, Ragnar Frisch, Bjørn Føyn, Endre Berner and Carl Jacob Arnholm were sent to Grini concentration camp.
[1] Arnholm also served as a "judicial advisor" to the association Norwegian Brewers from 1933 to 1968, and was an Acting Supreme Court Justice in several periods between 1935 and 1939.
He was elected as a member of the Norwegian Academy of Science and Letters in 1936, and held honorary degrees at Stockholm College (1957) and the University of Copenhagen (1959).