Ambassador ad Hon. Clis entered the Diplomatic Service in 1973. He served in various capacities in Brussels, Bucharest, London, Istanbul, San Francisco. From 1996 to 1998, he served as Director of Turkey and Cyprus Department at MFA. In 1998, he was appointed as Ambassador to the French Republic in which he served until 2002. He was MFA Deputy Director General and Director of the Turkey Department in 2002 and in 2003. From 2003 to 2005, he served as Director General for Political Affairs at MFA. In 2005, he was appointed as Ambassador to the Russian Federation where he served until his retirement in 2008.

From 2009 to 2015, he was a Special advisor for International Activities to the Federation of Greek Enterprise and Industry (SEV). Also, in 2009, he joined the Greek Turkish Forum. From 2014 to 2018, he worked as a Lecturer on Foreign Policy at Hellenic National Defense College.