In addition to contributing to Nigerian and African law, Elias had long been active in the field of international law. He was a member of the United Nations International Law Commission from 1961 to 1975, he served as General Rapporteur from 1965 to 1966 and was its chairman in 1970. He was the leader of the Nigerian delegations to the conference held to consider the Draft Convention on the Settlement of Investment Disputes between States and Nationals of Other States in 1963 and to the Special Committee on the Principles of International Law concerning Friendly Relations and Co-operation among States in 1964. He was a member of the United Nations Committee of Experts, which drafted the constitution of the Congo, 1961–1962. He also helped to draft the charter of the Organization of African Unity (OAU), and its Protocol of Mediation, Conciliation and Arbitration. Elias also represented the OAU and Nigeria before the International Court of Justice in the proceedings concerning the status of Namibia. He was elected as an associate member of the Institut de droit international in 1969. He was Chairman of the Committee of the Whole at the Vienna Conference on the Law of Treaties (1968–1969).