In 1660, he succeeded to the patriarchal throne on the death of Christophorus II with the approval of his reigning Muslim cousin, Vakhtang V (Shah Nawaz Khan).

Domentius was a supporter of Vakhtang's policy aimed at enhancing central authority at the expense of self-minded nobility, but he energetically opposed the Iranian customs prevailing at the royal court of that time.

[3] Domentius' authority extended only to eastern Georgia, with the western Georgian church running its own affairs as a result of the past political and ecclesiastic fragmentation.

Immediately following his accession, Domentius embarked on a program of reorganizing perishes, building new churches, such as in Mchadijvari, and restoring older ones, such as Anchiskhati in Tbilisi, to which he attached a bell tower.

He was also responsible for acquiring the venerated icon of the Savior brought from the defunct Ancha monastery to Tbilisi and earning new land estates for the Patriarchal Cathedral of Mtskheta.