A product of a diplomatic family, he studied law in Geneva and entered the Swiss Federal Department of Foreign Affairs in 1956.
He began his diplomatic career with posts in Bogotá, Washington, D.C., Warsaw, The Hague, and the United Nations in New York City.
[1] In 1984, Brunner was involved in secret talks held in Switzerland aimed at restoring ties between the United Kingdom and Argentina which were severed during the 1982 Falklands War.
Brunner caused a stir in 2002 when his memoirs described UK Prime Minister Margaret Thatcher as "vindictive" towards the newly-democratic Argentina during those 1984 talks.
In 1991, United Nations Secretary-General Javier Pérez de Cuéllar named Brunner to be the U.N.'s envoy to the Middle East.