Thieß joined the Bertelsmann Stiftung in 2004. As a senior advisor with the project Global Economic Dynamics (GED) he specializes in macro-economic studies and economics. He is currently concentrating on the causes and effects of financial and economic crises, the chances and risks of globalization, and the public debt and euro crisis. Thieß studied economics in Paderborn and Kiel, Germany. He then took up a position as a research assistant with the Institute for Theoretical Economics at the Christian-Albrechts-University in Kiel, Germany. He later became a research assistant and economics lecturer at the University of Applied Sciences in Heide, Germany. Thieß was a project adviser with the DAG-Forum Schleswig-Holstein (then called ver.di-Forum Nord) in Kiel and later became its managing director. In addition to his work for the Bertelsmann Stiftung, Thieß is a lecturer at the European University Viadrina in Frankfurt (Oder), where he specializes in micro and macro economics.