Jeremiah O'Flynn, born in County Kerry in 1788, had studied with the Franciscans and become a Cistercian monk at Lulworth in England; he was appointed prefect apostolic for New South Wales and arrived in Sydney on 9 November 1817, ahead of his papers. He began baptising, hearing confessions, marrying and saying Mass in Catholic homes. Governor Macquarie, who feared he might stir up the Irish convicts and heard of conversions, ordered him out. Four hundred free Catholics and some leading Protestants petitioned for him to stay; the governor had him arrested and put aboard the David Shaw, which sailed on 20 May 1818 (Australian Dictionary of Biography).
He left the Blessed Sacrament behind, reserved in a pyx in the house of one of the Catholic families — the Davises' or the Dempseys'; the accounts differ, and the Archbishop of Sydney, preaching at its bicentenary in 2018, declined 'to referee that'. The Catholics of the colony, without a priest, kept a daily vigil before it, said the Rosary there, taught the children their catechism and prayed Sunday Vespers. Some months later, by the Archbishop's account, the chaplain of a visiting French naval ship consumed the Sacrament and said Mass for them afresh; the parish's own history places that in late 1819.
The first official Catholic chaplains, John Joseph Therry and Philip Conolly, arrived in 1820. St. Patrick's Church on Church Hill was raised two decades later, in the old heart of Catholic Sydney — 'where our religion was cradled and concealed, its mysteries worshipped', in Archbishop Polding's words. The story rests largely on accounts written down long afterwards. A pyx said to date from 1818 was shown at the bicentenary; its history is not established.