He began his career at the Institute for National Issues (1961–1964).[3] From 1967 to 1972, he served on the Executive Council of the Slovene government. He was with the University of Ljubljana from 1976 to 1988 in capacity of professor, vice dean and finally dean. From 1983 to 1986, he was with the Addis Ababa University as a professor of International Law. From 1989, he began serving as an ambassador, including the United States, India, and Austria, and, as a non-resident, Nepal, Mexico, and Brazil. He is an ambassador to the UN, IAEA, UNIDO, CTBTO, ODC, and OECD. As UN ambassador, he has served as elected president of the International Law Commission.[4] For three years beginning in 1997 he served the Ministry of Foreign Affairs as its state secretary.[3] From 2010 to 2013, he was president of the Slovenian Constitutional Court.[2] Since 2017 he has served as a senior advisor to the president of Slovenia.[5]
Petrič, Ernest (1966). The rights of national minorities as defined in the statutes of the communes. Ljubljana: Inštitut za narodnostna vprašanja. pp. 75–102. ISSN0034-0251. OCLC442596343.
Petrič, Ernest (1976). The principle of the right of peoples to self-determination. Thessaloniki: Institute of International Public Law and International Relations of Thessaloniki.
Petrič, Ernest (1977). Mednarodnopravno varstvo narodnih manjšin. Sociološka in politološka knjižnica (in Slovenian). Vol. 7. Maribor: Zalozba Obzorja. p. 426.
Petrič, Ernest; Pavel, Slamič; Karel, Šiškovič (1981). La positione giuridica internazionale della minoranza slovena in Italia. Gli Sloveni in Italia (in Italian). Trieste: Editoriale stampa triestina. p. 141.
Petrič, Ernest (1984). Pravica do samoodločbe : mednarodni vidiki. Sociološka in politološka knjižnica (in Slovenian). Vol. 16. Maribor: Obzorja. p. 301.
Rahten, Andrej; Šumrada, Janez; Petrič, Ernest; Oven, Jacqueline; Leskovar, Matej, translator; Bataković, Dušan T.; Granda, Stane; Maver, Aleš, 1978- (2011), Velikih pet in nastanek Kraljevine Srbov, Hrvatov in Slovencev = Les cinq grands et la création du Royaume des Serbes, Croates et Slovènes / Andrej Rahten, Janez Šumrada (ur., éds.); [prevodi Jacqueline Oven, Matej Leskovar], Studia diplomatica Slovenica (in Slovenian and French), vol. 2, Loka pri Mengšu, Ljubljana: Center za evropsko prihodnost, Znanstvenoraziskovalni center Slovenske akademije znanosti in umetnosti, p. 479, ISBN978-961-92839-3-6, ISSN1855-9174{{citation}}: |first5= has generic name (help)CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)