The diocese has responsibility for the western suburbs of Sydney and the Blue Mountains, in New South Wales.

On 5 May 2016, Pope Francis appointed Vincent Long Van Nguyen, OFM Conv to be its fourth bishop.

[citation needed] The following prelates have served as Bishop of Parramatta:[3] With origins of the first Mass occurring on the present day site of the cathedral going back to 1803, St Patrick's was extensively rebuilt after a 1996 fire devastated the original church established in 1854.

As the needs of the parish grew, a new church was built on the site in 1936, incorporating the existing tower and spire.

Designed in consultation with Romaldo Giurgola, the new cathedral, completed in 2003, has won the Sir Zelman Cowen Award for Public Buildings from the Australian Institute of Architects.