He was a member of the royal Mukhrani branch of the Bagrationi dynasty, born as a younger son of Levan of Kartli (Shah-Quli Khan) and his first wife Tuta Gurieli.

[3] In 1705, Domentius, then aged around 28, was elected the head of the Georgian Orthodox Church after the synod convened by his brother Vakhtang, regent of Kartli for his absent uncle, George XI (Gurgin Khan), accused the catholicos Eudemus II of "ignorance" and removed him from the position.

The Safavid government of Iran, claiming sovereignty over Kartli, tolerated Vakhtang's support of the church owing to the contribution of the Georgian royals fighting on the Afghan front.

[4][5][3] By the time of Domentius's accession, the Georgian church had been split into the two, eastern and western counterparts, reflecting the political division of the country back in the 15th century.

Inclined to underscore his hierarchical supremacy, the new prelate resumed using the title of patriarch, for a time forgotten by the Georgian catholicoi as their church had experienced decline under the Iranian hegemony.

He exploited his royal origin and wealth to restore the churches and monasteries across the country, commissioned copies of old manuscripts, had the Greek Breviary translated and published—one of the first books printed in Georgia—in Tbilisi in 1719.

The 18th-century European authors such as Judasz Tadeusz Krusinski and the Capuchin missionary Pierre d'Issoudun report that Domentius, while visiting Iran, offered to unfrock himself, marry and convert to Islam, hoping to accede to the throne of Kartli.

[6] While the trustfulness of these reports remain disputed to this day, the rumors were current in Domentius's time as suggested in the historical poem Bakariani written by the catholicos's companion Iese Tlashadze.