John Therry was born in Cork and was privately educated at St Patrick's College in Carlow.

His chief anxiety was the need of a church, and in view of the increase in the population of Sydney in future years, it was decided that it should be on a large scale.

Almost by chance the site on which St Mary's Cathedral now stands was granted by the government, subscriptions were given by generous people, including many non-Catholics, and by 1823 it had been agreed that if a fresh subscription were opened the government would give a sum "equal to the sum total of all such additional donations".

Father Power was appointed chaplain, a man in poor health, who was compelled at times to accept assistance from Therry, though the two men were unable to find a way of living amicably together.

He was much helped by a friendship he formed with a namesake, Roger Therry, who arrived in Sydney towards the end of 1829, held many important positions, and became a leading Roman Catholic layman.

Similar difficulties arose, but Darling had left at the end of 1830 and the arrival of the wise and just Governor Bourke gave new hope to the Roman Catholic community.

Ullathorne, who was young with a fine grasp of business, was at times critical of Therry's lack of this quality but realized how truly religious he was and how hard he had worked for his people.

In May 1834 John Bede Polding, the first Roman Catholic bishop in Australia was appointed and arrived in September 1835.

Difficulties also arose concerning the responsibility for church debts, and eventually Therry was suspended from all clerical duties.

He remained for two years in Tasmania and in August 1846 was transferred to Melbourne, where he gained a reputation for his charity and missionary work.