1906. His outstanding performance in the latter was noted by Pope Pius X, who told the young Agagianian: "You will be a priest, a bishop, and a patriarch." He was ordained priest in Rome on 23 December 1917. Despite the upheaval bought by the Russian Revolution, he thereafter served as a parish priest in Tiflis (Tbilisi) and then as pastor of the city's Armenian Catholic community from 1919. He left for Rome in 1921, after the Democratic Republic of Georgia was invaded by the Red Army. He later said he was not confined by the Bolsheviks as "they had many other things to do." In late 1921, Agagianian became a faculty member and assistant rector of the Pontifical Armenian College in Rome. He later served as rector of the college from 1932 to 1937. He was also a faculty member of the Pontifical Urban University from 1922 to 1932. Agagianian was appointed titular bishop of Comana di Armenia on 11 July 1935, and was ordained bishop on 21 July 1935, at the San Nicola da Tolentino Church in Rome. His episcopal motto was Iustitia et Pax ("Justice and Peace"). Armenian Catholic Patriarch On 30 November 1937, Agagianian was elected Patriarch of Cilicia by the synod of bishops of the Armenian Catholic Church, an Eastern particular church sui iuris of the Catholic Church. The election received papal confirmation on December 13, 1937. He took the name Gregory Peter (; Armenian: Krikor Bedros) and became the 15th patriarch of the Armenian Catholic Church, which had 50,000 to 100,000 adherents. All Armenian Catholic Patriarchs have Peter (Petros/Bedros) in their pontifical name as an expression of allegiance to the church founded by Saint Peter. According to Rouben Paul Adalian, the Armenian Catholic Church regained its stature in the Armenian diaspora under the "astute management" of Agagianian following the sizable losses in the Armenian genocide in the Ottoman Empire. As patriarch, he had immediate ecclesiastical jurisdiction over around 18,000 Catholic Armenians in Lebanon. Agagianian reportedly played a key role in keeping the Armenian-populated village of Kessab within Syria when Turkey annexed the Hatay State in 1939 by intervening as a representative of the Vatican. Agagianian inaugurated the Armenian Catholic church in Anjar, Lebanon in 1954 and founded a boarding house for orphaned boys there. He resigned the pastoral governance of the Armenian patriarchate on 25 August 1962, to focus on his duties at the Vatican.