He held various monastic and ecclesiastical positions, including being a general vicar of the Diocese of Mostar-Duvno in 1943 and a Provincial of the Franciscan Province of Herzegovina from 1943 until 1945, when he was murdered by the communist Yugoslav Partisans.

During World War II, Petrović helped Serbs, Jews and political dissidents, including the Yugoslav Partisans.

Petrović was born in Klobuk, Ljubuški in Bosnia and Herzegovina, at the time part of Austria-Hungary, into a family of Herzegovinian Croats, and was baptized as Grgo.

[3] Under the mentorship of Prince Maximilian of Saxony,[5] he earned his PhD, with a dissertation titled Disquisitio historica in originem usus Slavici idiomatis in liturgia apud Slavos ac praecipue Chroatos dissertatio on 31 January 1908.

[7] During the Austro-Hungarian rule in Bosnia and Herzegovina, Petrović supported Croatian political alliance with the Serbs, contrasting the idea of Archbishop Josip Stadler.

[7] Petrović's doctoral thesis titled "Disquisitio historica in originem usus Slavici idiomatis in liturgia apud Slavos ac praecipue Chroatos dissertatio" from the University of Fribourg was published in Latin by the Croatian Joint-stock Printing House in 1908.

His doctoral thesis was translated into Croatian by Šime Demo and republished as a chapter titled "Povijesno istraživanje o početku uporabe slavenskoga jezika u liturgiji kod Slavena, napose Hrvata" in the biographical book about him authored by Ante Marić titled Leo Petrović prvi hercegovački franjevac doktor znanosti (Leo Petrović – the first Franciscan Doctor of Science), published in 2008 by the Franciscan Province of Herzegovina.

[10] Petrović also wrote about the Illyrian priests in Herzegovina, publishing four articles on them in the Catholic periodical "Kršćanska obitelj" (the Christian family) in 1939.

The next day, he and Cvitan Spužević, a notable Croat lawyer from Mostar, organised peace talks between the warring sides.

The authorities of the newly established Independent State of Croatia (NDH) started mass arrests and killings of Serbs between 25 and 26 June 1941.