Thomas Greminger studied History, Economics and Political Science at the University of Zurich. He obtained a Ph.D. degree in History in 1989. 

Mr. Greminger started his diplomatic service for the Federal Department of Foreign Affairs in 1990. In 1992-1998, he worked as a diplomatic assistant. He then worked as Deputy Director General, and later Director General of the Policy and Research Department in the Swiss Agency for Development and Cooperation, the Agency for International Cooperation of the Federal Department of Foreign Affairs. In 1999-2001, Mr. Greminger held the position of Coordinator for matters of Swiss Development Cooperation and acted as Chargé d'Affaires in the Swiss Embassy in Maputo, Mozambique. From 2002 to 2004, he worked as the Deputy Director General of the Human Security Division and Director General of the section for Peace Policy Greminger was later promoted to  the rank of Ambassador. In 2004-2010, Greminger directed the Competence Centre for Peace, Human Rights, and Humanitarian and Migration Policy. From 2010 to 2015, Greminger was the Permanent Representative of Switzerland to the OSCE and Swiss Ambassador to the UN - serving as Chair of the Permanent Council during Switzerland’s 2014 OSCE Chairmanship. In 2014, he became Director General of the Human Security Division. In 2015, he became Deputy Director General of the Swiss Agency for Development and Cooperation.

 He holds the rank of Lieutenant Colonel in the Swiss Armed Forces.

On the 18th of July, 2017 Mr. Greminger was appointed Secretary General of the OSCE for a three-year term.