The Roman Catholic Diocese of Penang is situated in the northern as well as the east coast region of Peninsular Malaysia covering 4 northern states, namely Perlis, Kedah, Penang and Perak as well as the east coast state of Kelantan. It was created on 25 February 1955 together with the Archdiocese of Kuala Lumpur. It is under the ecclesiastical province of Kuala Lumpur.

The Roman Catholic Metropolitan Archdiocese of Kuala Lumpur is an ecclesiastical territory or diocese of the Roman Catholic Church in Malaysia. It was erected as the Diocese of Kuala Lumpur by Pope Pius XII on 25 February 1955, and was elevated to the rank of a Metropolitan Archdiocese on 18 December 1972, with the suffragan sees of Malacca-Johor and Penang. It also administers the capital city of Malaysia, Federal Territory of Kuala Lumpur as well as the federal administrative centre of Putrajaya and the urbanised states of Selangor and Negeri Sembilan in the central region as well as Pahang and Terengganu on the East Coast. The archdiocese's Mother Church and thus, seat of its Archbishop, is St. John's Cathedral. It was one of the three Roman Catholic archdioceses in Malaysia, with the ecclesiastical archdioceses of Kota Kinabalu and Kuching, both at the Borneo Islands.