Dr. Joseph Mar Dionysius is the Metropolitan of the diocese, whose head office is in Bishop's House, Cross Junction, Kadappakada, Kollam, Kerala, India.

According to tradition, Thomas the Apostle arrived in the city and founded a church which is now underwater.

Kollam is one of the seven dioceses created after the Mulanthuruthi Syrian Christian Association (synod) of 1876, led by Patriarch of Antioch Ignatius Peter IV; the other dioceses are Kottayam, Kandanadu, Angamali, Niranam, Thumpamon, and Kochi.

[1] Vattasserril Geevarghese, Geevarghese II (when the diocese's head office was in the Kundara seminary), Alexios Mar Thevodosios of Bethany (who became metropolitan in 1938),[1] Mathews I, and Mathews II followed.

[1] Mathews I moved the diocese's head office from Kottappuram Seminary in Kottarakkara to Cross Junction, near Kadappakada, where the bishop's house (aramana) and St. Thomas Orthodox Syrian Cathedral were built.