Arne Sejersted was a crew member of the Mosk II at the 1920 Olympics, the only boat competing in the 10 metres, 1919 rating tournament. As such, by sailing over in each of three races, he and his fellow crew, Charles Archer Arentz, Willy Gilbert, Robert Giertsen , Halfdan Schjøtt, Trygve Schjøtt, and Otto Falkenberg automatically won the gold medal. Sejersted was a member of Kongelig Norsk Seilforening-Kristiansand and, by career, was a dentist, a vocation that he was still pursuing well into his 50s. Although he was born in Trondheim, he later moved to Agder county to practice his craft in Kristiansand and spend the rest of his life.