Son of a church minister, in 1914, he started his studies at the Toronto University and in 1916, he volunteered to serve with a hospital unit. Following the war, he studied history at Oxford University. In 1928, he started his public service in the Canadian Department of External Affairs, serving on a number of commissions and participating in the Hague Conference on Codification of International Law, the Geneva World Disarmament Conference (1933–1934) and in sessions of the League of Nations. His career moved forward rapidly.

During his stay in Washington in 1943–1945, he participated in the establishment of the UNRRA (United Nations Relief and Rehabilitation Administration) and in talks on the creation of the FAO (United Nations Food and Agriculture Organization). He also took part in Dumbarton and San Francisco conferences on the establishment of the United Nations.

In 1948, he took over the post of the Secretary of State for External Affairs. He was head of the Canadian delegation to the UN (1946–1956). As chairman of the General Assembly’s Special Committee on Palestine, he laid the foundations for the creation of the state of Israel in 1947. During the Suez Crisis of 1956, he proposed a resolution which established a United National Emergency Force (UNEF) to supervise the withdrawal of the British, French and Israeli armed forces from Egypt after the Suez War.