The Saint Leon Parish, as well as all other Armenian Apostolic Orthodox Churches, is functioning under the greater jurisdiction of the Mother See, The Holy See of Etchmiadzin. Meaning "where the only-begotten descended", Etchmiadzin was established as the Mother See in 303 AD shortly after Armenia's conversion to Christianity in 301 AD (making it the first state to officially adopt Christianity as the national religion).

According to tradition, the founding Saint of the Armenian Church, Saint Gregory the Enlightener of Cesarea, saw Jesus in a dream descend to the earth. It was on this spot that he commanded Saint Gregory to build his church. The church building itself still stand today (although many additions have been made since that time).

Today Holy Etchmiadzin is a religious complex, which includes the cathedral, monastery (the Brotherhood of Saint James), seminary, as well as other church buildings and is the administrative seat of the present Supreme Patriarch, His Holiness Karekin the First Catholicos of all Armenians. The Supreme Patriarchate, or Holy See of Etchmiadzin, maintains jurisdiction over the Armenian Patriarchates of Jerusalem and Constantinople (Istanbul) as well as over thirty dioceses spanning all continents.