Josko has an extensive career in public and private sector. He started his diplomatic career in the Ministry of Foreign Affairs of Croatia, where he held numerous positions from the desk officer in the International Law Department to the Deputy Minister of Foreign and European Affairs. He headed several departments with the Ministry and served as the Chief of Cabinet of the Minister and Director of the EU Directorate, as well as the Secretary-General of Croatian Negotiation’s Team for Accession to the EU. He was in charge of organising and conducting the referendum on Croatia’s accession to the EU, as well as the Government public campaign that preceded the referendum. He continued his career in New York and Brussels where he held the positions of political councillor to the Croatian Mission to UN and Deputy head of Mission to NATO. He was twice elected to the Croatian Parliament and appointed as the Chief of Staff of the Office of the President of the Republic. He was also a candidate of the Social Democratic Party at the elections for the European Parliament. While working in private business as the Secretary General of Atlantic Group, he was the President of an NGO called the United Nations Association. He also served as a Member of the University Council of the University of Zagreb and the Dean of the Dag Hammarskjold University College of International Relations and Diplomacy.