In his second parliamentary term, he chaired the Protocol Committee. In 1905, he chaired the "Special Committee" that prepared the establishment of a Norwegian consulate service, and thus the dissolution of the union between Norway and Sweden. When the union was dissolved and Norway could appoint its own diplomats, Prebensen became the ambassador ("minister") to the Russian Empire in 1906. He remained so until after the Russian October Revolution, when diplomatic ties to Russia were severed.