In 1975, he began his career in Vietnam's Ministry of Foreign Affairs. He was appointed Deputy Director-General for International Organisations in 1993. In 1995, he was appointed as Ambassador – Permanent Representative to the United Nations Office and Other International Organisations in Geneva.[1] In 1997, he was appointed as Ambassador – Deputy Permanent Representative to the United Nations at Headquarters. Since February 17, 2004, he has been Vietnam's ambassador to the United Nations in New York City.[2] He held this office from 1995 to 1997 for the UN institutions in Geneva and as a deputy in New York City from 1997 to 1999.[2] He was the President of the United Nations Security Council in July 2008[5] and October 2009.[4][6] He was nominated ASEAN Secretary-General by the government of Vietnam, a post which he took over on January 1, 2013. The ASEAN leaders endorsed him as ASEAN Secretary-General for 2013–2017 in a ceremony at the bloc's headquarter in Jakarta on January 7, 2013.