They were Irishman, transported to New South Wales for their complicity in the Irish Rebellion of 1798. As they were not officially appointed clergyman, they were not welcomed by the Colonial Administration as it was thought that they would incite rebellion in the large number of Irish convicts.
The first Catholic Masses in the colony were therfore celebrated in secret, as depicted in the stained glass window in St Mary's Cathedral, Sydney (first window on the western side of the nave). This is an early the celebration of the Eucharist by Father James Dixon in the kitchen of a cottage in 1803 with a lookout at the door.
Father Dixon celebrated the first official Mass in the colony on 15 May 1803 following a procalmation by Governor Philip Gidley King permitting Catholic worship.
There is an exhibition in the crypt of St Mary's Cathedral, with a set of silk vestments known as the "Convict Vestments" probably used by Father Dixon.
While researching the early days of the Catholic Church in Australia, I was particularly interested in the official correspondance between the main players, including the NSW Colonial Administraion, the British Government and the priests themselves. This is found in various despatches of Series One of the Historical Records of Australia [published by the Library Committee of the Commonwealth Parliament ].
Using these primary sources, I have complied a "History of the Roman Catholic Church in the Colony of New South Wales 1800 -1836".
You can find this on the website of History Services NSW at: