Sauer has served as Head of the Unit for UN and General Global Affairs of the Political Department at the Ministry for Foreign Affairs since 2007.
Sauer entered the Ministry for Foreign Affairs in 1995 and has worked in the Political Department, Department for External Economic Relations, Department for Communications and Culture, and Department for Europe. He served as Director of the Unit for the Western Balkans in 2005.
His diplomatic career includes postings to the Finnish Embassy in Zagreb and the Permanent Mission of Finland to the UN in New York.
In 2003-04, Sauer was Senior Adviser to Harri Holkeri, Special Representative of the Secretary General in the United Nations Interim Administration Mission in Kosovo (UNMIK). In 2004-05, he served as Head of the Strategic Analysis and Research Unit at UNMIK.
In 2005-07, Sauer served as Senior Adviser to the Special Representative of the Secretary General, Martti Ahtisaari, in the Kosovo Future Status Process (UNOSEK) in Vienna.