The mission's responsibilities included providing a peacekeeping force to maintain security and order; facilitating and co-ordinating relief assistance to the East Timorese; facilitating emergency rehabilitation of physical infrastructure; administering East Timor and creating structures for sustainable governance and the rule of law; and assisting in the drafting of a new constitution and conducting elections.

[1] UNTAET was established on 25 October 1999, the mission was led by Sérgio Vieira de Mello of Brazil (Special Representative of the Secretary-General for East Timor).

The military and police forces were transferred to the newly created United Nations Mission of Support to East Timor (UNMISET).

France also sent special forces who joined the ANZACs on the first day, as well as contingents from Brazil, Canada, Denmark, Italy, Kenya, Japan, Malaysia, Singapore, South Korea, Thailand, the Philippines, Sweden, and the United Kingdom.

While the United States supported the transition authority, it did so mainly by underwriting contracts to replace destroyed infrastructure and thus avoided a direct military involvement, allowing the ANZAC led force to take the lead.