Sebastian Roßner studied law, history, economics and political science in Düsseldorf, Duisburg and Hagen. He completed his legal clerkship in Düsseldorf with a stay abroad of several months at Avvocati Marzari, Maestroni, Maggiora & Niccolini (today: italegal) in Verona. From 2004 to September 2018, Sebastian Roßner worked at the Chair of Public Law, Legal Theory and Sociology of Law of Prof. Dr Martin Morlok and at the Institute for German and International Party Law and Party Research. In addition to his work in research and teaching, he has been involved in numerous legal representations in the field of constitutional law and party law. In October 2018, he joined the Cologne office of LLR as a lawyer.

Sebastian Roßner works in various areas of public law. He primarily advises on state and constitutional law and political law, such as party law. He also specialises in public procurement law, public building and planning law and municipal law.

Sebastian Roßner holds lectures and seminars for various institutions in the areas of state organisation, political parties and foreign trade law. As an author, he has published numerous articles on various areas of law in various specialist journals, online magazines and blogs.

When Sebastian Roßner is not working, he spends time with his family and friends, reads, listens to music or takes photographs.