Through his schooling in Germany, Imerslund got traditional Germanic values such as nationalism and respect for traditions. Germany in the 1920s was characterized by a lot of social unrest and an irreconcilable struggle between different ideological factions, which made a strong impression on Imerslund.
In 1934, he joined the National Socialist Workers' Party of Norway (NNSAP).
In 1936, Imerslund was part of an attempt to spy on the communist Trotsky, who had been granted residence in Norway by the Nygaardsvold government. Imerslund was fined for his participation in the operation.
Imerslund married Liv Asserson on March 26, 1938, with whom he had two children.
During World War II, he participated on the German side during the campaign in the Soviet Union as a volunteer in the Waffen-SS. After the campaign, he was transferred to the 6th SS Mountain Division "Nord" in Finland, where he was severely injured.
Imerslund died at Aker Hospital in Oslo on 7 December 1943.