Studying in the United States, Menkerios earned a bachelor's degree from Brandeis University and a master's degree from Harvard University. During the period from 1991 to 2000, Menkerios was Eritrea's Ambassador to Ethiopia and the Organisation of African Unity, its Special Envoy to Somalia and the African Great Lakes region, and was Eritrea's Permanent Representative to the United Nations. Later, as Senior Adviser to Moustapha Niasse, the Special Envoy of the United Nations Secretary-General to the Inter-Congolese Dialogue, he assisted Niasse in the mediation process that led to the Global and All-Inclusive Agreement, which was signed on December 17, 2002 and marked the end of the Congolese Civil War.