A serving United Nations staff member, Michael Zammit Cutajar was assigned in 1991 to set up in Geneva the interim secretariat supporting the intergovernmental negotiations that produced the United Nations Framework Convention on Climate Change (UNFCCC). After the entry into force of the Convention and its first Conference of the Parties (1995), he was appointed head of the permanent Convention secretariat, with the title of Executive Secretary and the rank of Assistant Secretary-General of the United Nations. He rebuilt the secretariat at its new home in Bonn in 1996 and headed it there until his retirement from the United Nations in 2002.

Between 2002 and 2011, Mr. Zammit Cutajar advised the Government of Malta on climate change and international environmental issues, serving as Malta's Ambassador on Climate Change in the work of the European Union and the UNFCCC. In that period, he also participated in bodies providing advice to the World Bank and to the President of the European Commission.

As Malta's Ambassador, he was elected to be Chair of the Ad Hoc Working Group on the Kyoto Protocol (2006) and Vice-Chair and Chair of the Ad Hoc Working Group on Long-term Cooperative Action (2008-2009) the two negotiating tracks then aiming at agreement on stronger international action to address climate change. In the latter functions, coming to a close at UNFCCC COP 15 at Copenhagen, his working base was the Institute for Sustainable Development and International Relations (IDDRI), in Paris.

Since resigning his ambassadorial functions in 2011, Michael Zammit Cutajar has continued to take part in discussions around the international negotiations on climate change.

During 2014-2015, he renewed his relationship with IDDRI, providing advice on those negotiations in the context of IDDRI's mission to provide substantive support to France's Presidency of UNFCCC COP 21. In that capacity, he was included in the French delegation to the UNFCCC.  Also in 2015, he advised the Government of Malta on the climate change content of the Commonwealth Heads of Government Summit hosted by Malta that year and led the drafting of the Commonwealth Leaders Statement on Climate Action.

He stepped back from the climate change scene at the end of 2015.

Mr. Zammit Cutajar has been awarded honours for his work in the area of climate change: Member of the Order of Merit of Malta (2007), Knight's Cross in Hungary's Order of Merit (Civil Division) (2009), Chevalier de la Legion d'Honneur, France (2010), and Cross of the Order of Merit of the Federal Republic of Germany - Verdienstkreuz am Bande - (2013).

Mr. Zammit Cutajar  a citizen of Malta, born 1940 - was educated at St. Edward's College, Malta, and the University of London. Before being parachuted into the climate change arena, he had devoted most of his career to work in and around the United Nations on international cooperation for development and environment.
His earlier United Nations postings were with the UN Conference on Trade and Development (1967-71, 1974-78, 1986-91), the UN Conference on the Human Environment (1971-72) and the UN Environment Programme (1973-74). Between 1982 and 1985, he undertook assignments for the United Nations at its Geneva and New York offices and on mission in Iran.

His work outside the United Nations framework included assignments with the Uganda Development Corporation, Kampala (1963-65), the Overseas Development Institute, London, UK (1965-67) and International Foundation for Development Alternatives, Nyon, Switzerland (1978-81).