Professor Marko completed his studies in Law and English at the University of Graz in 1977, earning his title of Dr. iuris (Doctor of Law) and B.A. in English. He then went on to complete his post-graduate studies in political sciences and sociology at the University in Munich, before joining the University of Graz as a member of the Law Faculty. In 1994, he obtained his Habilitation, and from 1997, he served as an assistant professor at the Law Faculty in the University of Graz, before becoming a full professor at the same institution in 2006. He was also a visiting professor at Rutgers School of Law, Camden, and gave lectures at the Summer School of the University of Bologna. From 2011 to 2016, he served as dean of the Law Faculty at the University of Graz.
Throughout his career, Professor Marko occupied important international positions such as Vice-Chairman of the Committee for International Relations of the Faculty of Law, University of Graz, as well as member of the executive boards of the Austrian Associations of Comparative Law, the Austrian Political Science Association and the Austrian Institute of East and South-East European Studies. He was also a member of the Association of the Professors of the German Constitutional Law, the Austrian UNESCO Commission, the forum of lawyers of the Alpe Adria region, the Research Institute of Еurореаn Law at the University of Graz, the Görres Society as well as the editorial board of the Europa Ethnica.
Professor Marko worked as the co-director of international research-programmes such as “Law аnd Revolution" sponsored by the Austrian Ministry of Sciences, and “Eastward Enlargement of the European Union: the case of the Czech Republic and Slovakia" at the Robert Schuman Сеntrе of the European University Institute, Florence. He was also a member of the Advisory Committee of the Framework Соnvеntiоn on the Protection of National Minorities, and co-director of the research-department on Ethnic Minorities and Regional Autonomies of the European Academy in Bolzano, Italy.
He served as an international Judge of the Constitutional Court of Bosnia and Herzegovina from May 1997 to May 2002.