He was then drafted for obligatory military service in the Yugoslav People's Army and served in Vis and Šibenik in Croatia from 1979 to 1980.

After leaving the military, Štironja studied at the High Philosophical-Theological School in Sarajevo, the capital of Bosnia and Herzegovina, from 1980 to 1986.

[3] Štironja was ordained a priest by the Bishop of Mostar-Duvno and the Apostolic Administrator of Trebinje-Mrkan Pavao Žanić on 29 June 1986.

[3] In 1988, not long after becoming a priest, Štironja applied himself for missionary work and prepared for half a year in London for missions in Africa and studying English.

[1] While serving in Canada, Štironja edited the parish bulletin and regularly aired a Sunday message for Croatian Catholics from the Radio of Toronto.

[2] In October 2016, Štironja was appointed the parish priest in Studenci, Ljubuški and the rector of the Sanctuary of the Most Holy Heart of Jesus.

[1][5] The diocese was administered by the archbishop of Bar, Rrok Gjonlleshaj, since the retirement of the last bishop of Kotor, Ilija Janjić, in 2019.

His principal consecrator was the archbishop of Split, Marin Barišić, while Gjonlleshaj and the bishop of Mostar-Duvno, Petar Palić, served as co-consecrators.

[5] On 31 January 2023, Štironja was appointed the bishop of Poreč-Pula, succeeding Dražen Kutleša, who served as the diocese's apostolic administrator since 2020.