Professorship, Parliament and United Nations
After the war Hambro specialized in international organizational work. He was a Norwegian delegate to the San Francisco Conference in 1945, and led the United Nations judicial office until 1946. In 1946 he issued the Charter of the United Nations. Commentary and documents together with Leland Goodrich. From 1946 to 1953 he was a secretary at the International Court of Justice in the Hague.
He was then a research fellow at the Norwegian School of Economics from 1953, visiting scholar at the University of California in 1958 and professor of jurisprudence at the Norwegian School of Economics from 1959 to 1966. Academic publications in the Norwegian language include Norsk fremmedrett (1950), Folkerettspleie (1956), Jurisdiksjonsvalg og lovvalg i norsk internasjonal kontraktsrett (1957) and Arbeidsrett (1961). He also wrote volumes II, III (spanning two books) and IV (spanning two books) in the series The Case Law of the International Court of Justice together with Arthur W. Rovine.
He was also elected to the Parliament of Norway from Bergen in 1961, and was re-elected in 1965. He served his first term in the Standing Committee on Justice, and then entered the Standing Committee on Foreign Affairs.
In 1966, however, he aborted his political career to become the Norwegian permanent representative to the United Nations. He chaired the Sixth Committee (Legal Committee) at the 22nd United Nations General Assembly in 1967. He was the 25th President of the United Nations General Assembly from 1970 to 1971. 122 delegations voted for Hambro with 2 votes against his candidacy. He underlined that "peace, justice and progress" will be topics during his presidency in which he wanted to strengthen the organization. After his tenure as permanent representative ended, he continued serving the Ministry of Foreign Affairs and was the Norwegian ambassador in Geneva, to EFTA and various UN organizations. From 1976 he was the Norwegian ambassador to France. He also served on the United Nations International Law Commission from 1972. He died in 1977.
Hambro was also a board member of the Institute for Comparative Research in Human Culture and the Nansen Foundation, and from 1960 to 1966 vice president of the Norwegian Red Cross.
He chaired the appeals board of the Council of Europe, and was a member of the appeals board of the Organisation for Economic Co-operation and Development. He presided over the Permanent Conciliation Commission for the Federal Republic of Germany and the Netherlands, and was a member of the Institute of International Law, the Permanent Court of Arbitration, and the Franco-German Arbitral Tribunal for the Saarland.
He received honorary degrees at Brandeis University, Columbia University, Luther College, Seton Hall University, University of Toronto, Wagner College and Yale University. He was decorated as a Commander with Star of the Order of St. Olav (1970), and received the Grand Cross of the Order of the White Rose of Finland, the Order of the Yugoslav Star and the Order of Ouissam Alaouite.
