On 17 May 1933, with Vidkun Quisling he founded the Nasjonal Samling, a political party based on Germany's Nazi Party. He and Quisling devised a programme of mostly very right-wing policies that included the outlawing of revolutionary parties, the suspension of the voting rights for people in receipt of social welfare, agricultural debt relief and an audit of public finances. Hjort became leader of the Hirden, the paramilitary wing of the Nasjonal Samling party that was modeled on the German Sturmabteilung, the Nazi "Brownshirts". In 1937 Hjort broke with Quisling and left Nasjonal Samling.
Resistance during World War II
After the German occupation in 1940, Hjort held lectures in the German-controlled Norwegian Broadcasting Corporation, alongside individuals like Albert Wiesener, Jonas Lie, and Ranik Halle. He was arrested by the Gestapo in 1941 on the orders of Josef Terboven, the German Reichskommissar for Norway, after Hjort published a scholarly article in a journal of Norwegian law that openly criticised the German occupation. He was imprisoned, first in Oslo and then in Berlin. After being released, Hjort and his family carried out important resistance work in Germany, playing a crucial role in the first stages of the White Buses operation. It is estimated that this operation saved 15,345 prisoners from death in concentration and prisoner camps; of these, 7,795 were Scandinavian. In particular, 423 Danish Jews were saved from the Theresienstadt concentration camp inside German-occupied territory of Czechoslovakia, contributing significantly to the fact that the casualties among Danish Jews during the Holocaust were among the lowest of the occupied countries of Europe.
Post-war career
After the war, Hjort fought as a supreme court lawyer for the artistic freedom of controversial artists and for the natural legal rights of homosexuals. In 1957, in one of the most famous and widely debated court cases in Norwegian post-war history, Hjort was the defense lawyer for novelist Agnar Mykle, who was accused of immoral and obscene writing in his books. Hjort was a long-term leader of Riksmålsforbundet, an association that fought for the free evolution of the Norwegian language, in the direction of Riksmål. He was a prolific writer and lecturer and a frequent contributor to public debate. Among his books are Justismord, Dømt med rette?, and Demokrati og statsmakt. He also translated Kipling'sJust So Stories into Norwegian.