In 1842, Sydney was made an Archdiocese and Metropolitan See, with Hobart and Adelaide as suffragan dioceses. At the time, the Archdiocese of Sydney included the whole of the eastern portion of the continent, comprising what are now the States of NSW, Victoria and Queensland.

The suffragan dioceses of the present Province of Sydney and their dates of establishment are: Maitland-Newcastle (1847), Armidale (1862), Bathurst (1865), Lismore (1887), Wilcannia-Forbes (1887), Wagga Wagga (1917), Wollongong (1951), Parramatta (1986) and Broken Bay (1986).

There are currently 138 parishes in the Archdiocese of Sydney , under the care of around 190 diocesan priests. There are some 450 priests in all, including religious priests, working within the Archdiocese.

The home of Sydney's Catholic community and the mother church of Australia is St Mary's Cathedral .

It was built on the site of the first Catholic chapel in Australia and constructed in local sandstone. St Mary's is one of the largest Cathedrals in the world and the "Gothic Revival" style of its architecture is reminiscent of the great medieval cathedrals of Europe. The Cathedral is dedicated to the Blessed Virgin Mary, under the title of Immaculate Mother of God, Help of Christians.

There are around 600,000 Catholics in the Archdiocese, 32% of the total population