He obtained his doctorate in 1977 at the University of Freiburg with a dissertation on "Computer Crime and Criminal Law".
In 1994, he declined a call to the Chair of Computing Law at the University of Münster (now professor Thomas Hoeren).
In addition to his academic work, Sieber has been an expert consultant and advisor, especially in the areas of computer law.
He has also advised the Council of Ministers and the Parliamentary Assembly of the Council of Europe, the European Commission, the Research Ministers of the G-8 nations (Carnegie Group), the OECD, the United Nations, and the International Chamber of Commerce in Paris.
As a legal authority, he has written expert opinions for and been a consultant to the International Criminal Tribunal for the former Yugoslavia as well as the Department of Justice in Canada, the U.S. Senate, the Privacy and Civil Liberties Oversight Board of the U.S. government, and the National Police Agency of Japan.