On 14 November 1997, Secretary-General Kofi Annan announced the appointment of Sergio Vieira de Mello as Emergency Relief Coordinator (ERC) and Under-Secretary-General for Humanitarian Affairs effective January 1998.  Prior to joining OCHA, Vieira de Mello spent the majority of his career working for the United Nations High Commissioner for Refugees in Geneva, and served in humanitarian and peackeeping operations in Bangladesh, Sudan, Cyprus, Mozambique and Peru.

Mr. Vieira de Mello joined the United Nations in 1969 while studying philosophy and humanities at the University of Paris (Pantheon-Sorbonne).  He assumed his first United Nations high-profile position in 1981, when he was appointed Senior Political Adviser to UN forces in Lebanon.  Thereafter, he served in several important functions at UNHCR's Headquarters from 1983 to 1991 (Chef de Cabinet of the High Commissioner; Director, Regional Bureau for Asia and Oceania; and Director, Division of External Relations).

Between 1991 and 1996, he served as Special Envoy of the High Commissioner for Cambodia, Director of Repatriation for the United Nations Transitional Authority in Cambodia (UNTAC), Head of Civil Affairs of the United Nations Protection Force (UNPROFOR), and United Nations Regional Humanitarian Coordinator for the Great Lakes Region of Africa.  In 1996 he was appointed United Nations Assistant High Commissioner for Refugees.

Mr. Vieira de Mello was named Emergency Relief Coordinator immediately after the release of the Secretary- General's report on the reform of the United Nations (A/51/289, "Strengthening of the United Nations System Programme Budget for the Biennium").  In implementing the reports recommendations, he was required to undertake a far-reaching restructuring of the former Department of Humanitarian Affairs.  His efforts are widely credited with having made OCHA an effective and credible part of the United Nations Secretariat and the international humanitarian response system.

"Sergio", as he was known by the scores of government officials, UN staff members, and others who considered him a friend, was a pragmatic, experienced and widely respected diplomat. During his term with OCHA, he provided strong leadership to humanitarian agencies in a series of humanitarian crises that occured during his tenure as Emergency Relief Coordinator, inter alia in Afghanistan, in Central America (Hurricane Mitch) and West Africa.  He also made important progress on a number of key policy and advocacy issues, notably on the protection of civilian populations.  In 1999 he helped forge the United Nations response to the mass exodus of Albanians from Kosovo and was chosen by the Secretary-General to lead a UN mission to Serbia and Kosovo at the height of the NATO air campaign.  He was subsequently selected by the Secretry-General to act as his Special Representative at the outset of the UN mission in Kosovo, prior to the appointment of Bernard Kouchner.

In October 1999, he was appointed Special Representative of the Secretary-General and United Nations Transitional Administrator in East Timor (UNTAET).  He continued to serve as the ERC until January 2001 when Mr. Kenzo Oshima was appointed to succeed him. He stayed in East Timor until the United Nations turned-over the government to the East Timorese in May 2002.  On 12 September 2002, he was appointed United Nations High Commissioner for Human Rights.  In May 2003, he was asked by the Secretary-General to take a four-month leave of absence from his position as High Commissioner to serve in Iraq as Special Representative of the Secretary-General.

Sergio Vieira de Mello was tragically killed in the suicide bombing of the UN Headquarters in Baghdad on 19 August 2003 along with 21 UN staff.

He was married and had two sons.