The Archimandrite of New Canterlot is the de facto head of the Old Religion throughout the Isle of Yore. The archimandracy was established in 2081 AE by six clerics who fled Equestria during the catastrophe and found themselves cut off from the hierarchy. Formerly, the Monarch of New Equestria appointed the archimandrite, but the pious reforms of Queen Meridian resulted in a new system in which the religious authorities would select their own leader. The incumbent archimandrite is Harmonia XLII.

Under the rule of wizard-prince Bluestar the Brilliant, many clerics expected to serve a brief life-term as archimandrite in their old age. Bluestar notably excluded any who were known to use magical life extension. He is not known to have left records of his motivations for having acted in this way, although some historians speculate that he wanted to avoid creating a rival leader in the cloistered city.

After the fall of the cloister and consequent dramatic expansion of New Equestria's population (including its population of clerics), the office became more competitive, but the monarch still usually selected very elderly clerics who had distinguished themselves by a life of service to the state religion. Since Meridian's reform, however, the tendency has been for relatively younger and more energetic clerics to be selected. The archimandrite always takes a regnal name, usually relating to one of the elements of harmony or to some idea of civil welfare. The most popular regnal name is Harmonia/Harmonious, used by 42 of the 115 archimandrites who ruled since the establishment of the archimandracy. The second most popular is Pacifica/Pacificus with 24 archimandrites. The majority of the other names relate to individual Elements of Harmony, although there have been two archimandrites sharing a difficult to translate name relating to the establishment of a dependable postal service, and one whose regnal name was a brazen political statement criticizing a prime minister of Daystar.