Petersmann taught constitutional law at the Universities of Hamburg and Heidelberg and served as Professor of International and European Law at the
Universities of St. Gallen,
Fribourg, Geneva, and the
Geneva Graduate Institute. As a visiting professor, he has taught at institutions such as the
Hague Academy of International Law, the EUI Academy of European Law, the Xiamen Academy of International Law, and universities across Europe, North and Latin America, Asia, and Africa. In parallel to his academic work, Petersmann served as legal counsel to the
German government between 1978 and 1980, representing Germany in European and United Nations institutions. Petersmann was legal counsellor for the
General Agreement on Tariffs and Trade and worked as legal consultant for the
World Trade Organization from 1981 to 2025. He was among a small group of lawyers at the
General Agreement on Tariffs and Trade secretariat in
Geneva who helped reform the organization in the 1980s and transform it into the
World Trade Organization. University of Washington law professor Dongsheng Zang has called Petersmann, Jan Tumlir, an economics professor at the
Graduate Institute of International and Development Studies in Geneva, and US law professor
John Jackson "the GATT's major intellectual architects." == Scholarly work ==