His previous work includes expert advice on rule of law and democratization for the European Commission, the OSCE, and the Council of Europe, and to governments and international organizations working on issues related to the Balkans. Marko is the author of several scientific monographs including EU Rule of Law Promotion: Judiciary Reform in the Western Balkans (Routledge: 2016), and coeditor of Stagnation and Drift in the Western Balkans (Peter Lang: 2013) and Europeanization of the Western Balkans: The Failure of Conditionality? (Palgrave: 2018). He served as a Europe analyst for Freedom in the World.