Sir Michael is a member of the United Nations (UN) International Law Commission. He was the principal Legal Adviser to the Foreign and Commonwealth Office (FCO) between 1999 and 2006. During his 35 years as an FCO lawyer, Michael attended many international conferences, including the UN Conference on the Law of the Sea. He spent three years at the UK Mission to the UN in New York, dealing chiefly with Security Council matters.
Since leaving the FCO in 2006, Sir Michael has acted for many governments in cases before the International Court of Justice (ICJ), European Court of Human Rights (ECHR), International Tribunal for the Law of the Sea and inter-state arbitral tribunals. He has written extensively on public international law.