In 1970 he was transferred to the Central Bank as its Deputy Governor and later its Senior Deputy Governor till 1973 when he took up appointment as Ceylon's Ambassador to the European Economic Community, Belgium, Luxembourg and the Netherlands.
He was a Member (1965–1972) and chairman (1972–1974) of United Nations Committee on Development Planning; chairman, ILO Meeting on Evaluation of Comprehensive Employment Missions to Colombia, Kenya, Iran and Sri Lanka, (1973); Chief, United Nations Planning Mission to British Honduras, (1962); Special Representative of the Secretary General of the UN Conference on Human Environment, ( 1971–1972); Secretary-General of the United Nations Conference on the Least Developed Countries, Paris, (1981); Member, UN Panel of Eminent Persons on South Africa and Transnational Corporations, (September 1985); Member, UN panel of Eminent Persons on "The Relationship between Disarmament and Development", (April 1986); Team Leader, UNDP High Level Multi-Disciplinary Mission to Qatar, (13–26 April 1987); Chairman: United Nations General Assembly: Ad Hoc Committee of the Whole on an International Development Strategy for the Fourth Development Decade, (1989–90); Corea assumed post of Secretary-General of the United Nations Conference on Trade and Development on 5 April 1974 after he was appointed in 1973 for an initial term of three years by former United Nations Secretary-General Kurt Waldheim.
He was thereafter re-appointed three times, his fourth term covering the period December 1982 until the end of 1984.
As Secretary-General of UNCTAD and until the end of February 1985, Dr. Corea also held the position of Under-Secretary-General of the United Nations.
He held several positions, including the Chancellor of the Open University of Sri Lanka; Honorary Fellow, Corpus Christi College, Cambridge; Honorary Fellow, Institute of Development Studies, University of Sussex; chairman, Board of Governors, Institute of Policy Studies; Honorary Fellow, Bandaranaike Centre for International Studies; Fellow, National Academy of Science of Sri Lanka; Honorary President, Association of Former Civil Servants, Sri Lanka; Senior Adviser to the Ministry of Foreign Affairs; Joint Patron, Sri Lanka Economics Association; Patron, Symphony Orchestra of Sri Lanka.