He was, together with his wife Mona Juul, a key figure in the secret talks between PLO and Israel that led to the Oslo Accords in 1993.
From 1994 to 1996, he served as former Secretary-General, Boutros Boutros-Ghali's first Special Coordinator in the Israeli-occupied Palestinian sector.
In 1999, he was appointed as the UN Secretry-General Kofi Annan's personal representative to the PLO and Palestine Authority on the West Bank and the Gaza Strip. He is also the UN Special Coordinator for peace negotiations in the Middle East.