In the late 1980s, Cerar published a number of research articles and popular science articles, and started asserting himself as a critical legal thinker in the Slovenian public. In 1988, he was one of the authors of the book
Pravni memorandum: Vojaški tožilec versus Borštner, Janša, Tasić, Zavrl (Legal Memorandum: Military Prosecutor vs. Borštner, Janša, Tasič, Zavrl), and in 1989 he participated in writing
Pravni memorandum: Svoboda združevanja (Legal Memorandum: Freedom of Association). Both books called for the enforcement of the rule of law and democratic values, particularly in the light of the then non-democratic pressures of the regime on the democratisation process in Slovenia. Between 1993 and 1999, he was a correspondent of the Center for the Study of Constitutionalism in Eastern Europe (based at the New York University School of Law, and previously at the University of Chicago Law School and Central European University in Budapest), and he contributed periodic reports on the development of constitutionalism in Slovenia to the East European Constitutional Review. In 1993, he obtained his master's degree from the University of Ljubljana's Faculty of Law with the thesis
The Multidimensional Nature of Human Rights and Duties, and in 1999 his doctoral degree from the same faculty with the dissertation
(Ir)rationality of Modern Law. In 2000, he was appointed an assistant professor at the Faculty of Law; in 2005, he became an associate professor, and in 2011, he became a full professor. His areas of expertise included the theory and philosophy of law, comparative law, constitutional law, and the ethics of legal professions. He also lectured on the basics of law at the Faculty of Social Sciences at the University of Ljubljana (2006–2014), and on the theory of law and state at the University of Maribor's Faculty of Law (1995–1998). From 2002 to 2014, he annually delivered a set of lectures on basic legal concepts for translation students (specialising in German). In the 2011–2012 academic year, the University of Ljubljana's Student Council voted him the best teacher at the Faculty of Law. From 1989 to 2004, he was a mentor in the Legal Aid Service for Students, established by the University of Ljubljana's Student Organisation, where students from the Ljubljana Faculty of Law provided free legal assistance in study-related matters to other students. From 1994 to 2003, he was an external evaluator for the leaving exam subject in law. Between 1994 and 2014, he lectured on constitutional topics as part of the specialised training programme for state administration employees. From 2009 to 2012 he was chair of the examination committee for the state bar exam, and an examiner in constitutional arrangement, organisation of the justice system, and state administration, as well as the foundations of the EU legal order. From 2003 to 2014, he was vice president of the Slovenian Association for Legal and Social Philosophy. For six months in 2008, as a Fulbright Fellow, he taught comparative constitutional law at the Golden Gate University School of Law in San Francisco and pursued post-doctoral studies at the University of California School of Law at Berkeley. From 1990 to 1992, he was a member of the editorial board of
Časopis za kritiko znanosti (Journal for the Critique of Science). From 1995 to 2014, he was an editor of the research journal
Zbornik znanstvenih razprav at the Faculty of Law at the University of Ljubljana. From 2003 to 2014, he was a member of the editorial board of the Manet research series of the Ljubljana Faculty of Law, and from 2003 to 2006 a member of the editorial board of the magazine
Revus (covering European constitutionality) published by GV Revije. From 2002 to 2014, he was a member of the editorial board of the journal
Theory and Practice published by the Faculty of Social Sciences in Ljubljana, and of the book series
Legal Horizons issued by Cankarjeva Založba in Ljubljana. Between 2009 and 2013, he was a member of the Expert Board for Scientific Books and Journals at the Slovenian Book Agency, acting particularly as a reviewer of diverse social science contributions. From 2000 to 2018, in the annual polls conducted by the Ius Software portal (iusinfo.si), he ranked among the ten most influential Slovenian lawyers 17 times, and from 2011 to 2014 users of the Tax-Fin-Lex portal voted him the most influential Slovenian legal expert four times.
Constitutional and advisory roles In June 1990, Cerar, together with
Peter Jambrek,
Lojze Ude, and other experts, participated in drafting the initial proposal for launching the procedure for the adoption of a new Slovenian constitution put forth by the Presidency of the Republic of Slovenia. As an expert assistant, he coordinated the work of a 7-member expert group (members: Franc Grad,
Tine Hribar, Peter Jambrek, Tone Jerovšek, Matevž Krivic, Anton Perenič, and Lojze Ude), which prepared a working draft of a new
Slovenian constitution at Podvin Castle in August 1990. Between 1991 and 1992, he was Secretary of the Constitutional Commission of the Assembly of the Republic of Slovenia. In the same period, he also participated in drafting the following constitutional and legislative proposals: Amendments 99 and 100 to the then Constitution of the Republic of Slovenia; Basic Constitutional Charter on the Sovereignty and Independence of the Republic of Slovenia and the constitutional act for its implementation (25 June 1991); Constitution of the Republic of Slovenia and the constitutional act for its implementation (23 December 1991); and acts governing the elections into the National Assembly and the National Council, and presidential elections (1992). In the periods 1993–2007 and 2009–2014, Cerar served as an external adviser to the
National Assembly of the Republic of Slovenia for constitutional and legal matters, regularly coordinating the work of expert groups drafting opinions and constitutional amendments for the Constitutional Commission of the National Assembly. From the adoption of the Constitution (1991) to the moment he entered politics (2014), he participated in all discussions on constitutional amendments. He contributed to opinions on various constitutional and legal matters, particularly related to the electoral and wider political system,
referendums, immunity of deputies, and parliamentary rules of procedure. He was a member of expert groups tasked with the preparation of changes to rules of procedure and with the English translation of the Constitution, other constitutional acts, and the Rules of Procedure of the National Assembly. He advised the Legal Service of the National Assembly, Secretariat General, Office of the President of the National Assembly, and Constitutional Commission. After having served as deputy president since 2009, Cerar acted as president of the Judicial Council between 2010 and 2012. In this capacity, he participated in the procedures for the election, appointment, and discharge of judges and presidents of the courts, and those related to the promotion of judges, the immunity of judges and the incompatibility of the functions, disciplinary procedures against judges, and other procedures falling under the competence of the Judicial Council. He participated in several expert meetings with high representatives of judicial councils of European countries. As Slovenian representative to the European Network of Councils for the Judiciary (ENCJ), Cerar participated in the ENCJ project group tasked with establishing the level of public trust in the judiciary at the national and supranational levels in the 2010–2011 period, and in the 2011–2012 period in the ENCJ working group on judicial reform in Europe. ==Political career==