He held diplomatic positions in Vienna, Chicago, Antwerp, and Rotterdam, becoming vice consul in Minneapolis in 1931 and first legation secretary in Helsinki in 1934.
[3][4] Hallenborg enrolled at Stockholm University College the same year and graduated with a Candidate of Law degree on 31 January 1917.
Hallenborg became a lieutenant in the Svea Life Guards reserve on 28 October 1921, and an attaché at the Swedish legation in Vienna on 29 November of the same year.
[3] Hallenborg became vice consul in Minneapolis in 1931, first legation secretary in Helsinki in 1934, and director (byråchef) at the Ministry for Foreign Affairs in 1936.
[11] One of his first assignments as Consul General in London was to conduct a maritime inquiry with Captain Hommerberg of the Swedish oil tanker Divina,[12] which had collided with the British submarine HMS Truculent on 12 January 1950, resulting in the deaths of 64 people.
[5] After his retirement in 1960, Hallenborg and his wife settled on their farm by Lake Sommen in the South Swedish highlands.