The Diocese of Trincomalee - Batticaloa, is co-extensive with the Eastern Province. It consists of three civil administrative districts of Trincomalee, Batticaloa and Ampara. In fact, it is the largest of the 09 Province and 11 Diocese in extent, comprising almost 1/7 of the land-mass, i.e. 9,622.07sq.k.m3 From North to South, it is 300 k.m in length, and from East to West it is 125 k.m in breadth at its widest. In the north it is bounded by Ma oya and the fishing village of Pul moddai; in the south by Kumana Sanctuary, the reserves National Park for wild animals; in the east by sea and in the west by North-Central, Uva and Central Provinces. 

The Diocese of Trincomalee was erected by Pope Leo XIII, by his Apostalic

 Letter "In hact Beati Petri" dated 25th August 1893, comprising the whole of the Eastern Province and district of Tammankaduwa, all of which hitherto had been part of the diocese of Jaffna .