Mattis was FEPS’ new trainee and dealt with different tasks, including assistance in organising conferences, condensing information for publications and providing assistance in event support. He speaks German, English, French and Italian. 

Mattis holds a Master in European Governance from the University of Luxembourg, where he had the opportunity to study and work in a multinational environment. His Master’s thesis dealt with the Visegrád group dynamics concerning the Russo-Ukrainian war.