Having chosen the priesthood at a young age, Bostani enrolled in the Ain-Warca Maronite university where he studied Syriac, Arabic, Latin, Italian, rhetoric, philosophy, dogma, moral, canon law, the calendar and Church music.

He had only been teaching for a year that he was quickly called upon by his relative, the Archbishop of Tyre and Sidon Abdallah Bostani,[5] who named him his private secretary.

[4] On 28 July 1856, Maronite Patriarch Massad named him Coadjutor-Archbishop of Tyre and Sidon alongside his relative the Archbishop Abdallah Bostani who was becoming very old and weak.

[1] He immediately set out to preach in his diocese, repairing the various abuses and combatting the advances made by the Protestant missionaries in converting the people.

His biography states that he challenged, on four distinct occasions, the Protestant ministers to public discussions of faith and religious doctrine in front of six thousand people in the villages of Deir al-Qamar and Hasbeiya.

[4] Eugène Poujade, the French Consul of Beirut, travelled with his relative Bishop Abdallah Bostani to the 1845 synod in Dimane for the election of the new Patriarch of the Maronites.

"[6] Poujade states that Bishop Abdallah Bostani particularly regretted a painting of the Virgin Mary given to him by Emir Bechir II that had been burnt by the Druze in the conflicts.

[6] Following the sectarian violence which afflicted Mount Lebanon in the 1840s, Bishop Abdallah Bostani made "an impassioned plea to the women of France"[7] stating: "thus would our freedom be restored to us; are we not united with you, O French in heart?

[10] Though having gone into hiding to avoid being killed,[4] Archbishop Pierre Bostani was widely celebrated for having tried to save the Christians fleeing the massacres in Jezzine in 1860.

Within this college, thrice burnt by the Druze and twice rebuilt by the Bishop, he taught not only theology but also philosophy, history, Arab and Syriac literature, and jurisprudence".

[17] Bostani accompanied Maronite Patriarch Massad on his trip to Rome in June 1867 to attend the 1800th anniversary of the martyrdom of Saints Peter and Paul.

[18] Two years later, Patriarch Massad requested that Archbishop Bostani head the Maronite delegation that would attend the First Vatican Council in Rome in 1869.

The Maronite population wrote to the Ottoman Grand Vizier, as well as the ambassadors of France, Russia, Germany, Italy, the United Kingdom, and Austria to protest the arrest and exile of the Archbishop.

[20] Cardinal Guibert of Paris and Bishop Dupanloup of Orléans both summoned the French government to pressure the Ottoman Porte in reinstating Archbishop Bostani to his archdiocese.

Unfortunately for Bostani, the French ambassador in Constantinople and the British consul in Beirut, including the Apostolic Delegate Luigi Piavi, all sided with Rustem Pasha against him.