From 1960 to 1961, Wachuku served as first Ambassador and Permanent Representative of Nigeria to the United Nations in New York, as well as Federal Minister for Economic Development. He hoisted Nigeria's flag as the 99th member of the United Nations on 7 October 1960. Accordingly, Wachuku was instrumental to Nigeria becoming the 58th Member State of United Nations Educational, Scientific and Cultural Organization (UNESCO) on Monday 14 November 1960. Also, as First Ambassador of Nigeria to the United Nations, Wachuku represented the country at the independence celebrations of Tanganyika – now known as United Republic of Tanzania. At the United Nations, with support from UN Secretary General Dag Hammarskjöld, the member nations elected Wachuku the first African to chair a United Nations Conciliation Commission, making him Chairman of the Conciliation Commission for the Congo from January to March 1961. Initial proposal and nomination of Wachuku to be mediator in Congo came from Paul-Henri Spaak of Belgium, to which "Wachuku responded favorably on condition that U Thant, Cyrille Adoula and Moïse Tshombe agree."