Dr. Marušič was born in Koper. After graduating from Koper Gimnasium, he attended the University of Ljubljana, Faculty of Natural Sciences and Engineering graduating in mathematics. Afterwards he attended the Faculty of Medicine in Ljubljana, graduating in 1989. He specialised internal medicine and then worked at the Izola General Hospital, the University Clinic in Groningen and the Ljubljana University Medical Centre. In 2003, he enrolled in post-graduate studies in management of non-profit organisations at the Faculty of Social Sciences, University of Ljubljana. In December 2000, he was appointed State Secretary at the Ministry of Health of the Republic of Slovenia and re-appointed to the same position in 2004.
Prior to his position at the Ministry of Health, Dorjan was an adviser to the Director-General of the Health Insurance Institute of the Republic of Slovenia and engaged in a clinic as a specialist in cardiology. He is the author or co-author of more than 200 scientific works and has published over 350 popular articles. Dr. Marušič heads the Coronary Society of Slovenian Istria and is the vice-president of the expert council of the Association of Coronary Societies and Clubs of Slovenia. He is a member of the Slovenian Society for Emergency Medicine, the Slovenian Society of Anaesthesiology and Intensive Care Medicine, and the Slovenian Society of Cardiology.