In 1861, he left Ireland to serve as a Catholic missionary in the Australian bush country, where he founded a mission for the aboriginals at Burragorang, about 65 mi from Sydney.
[8] Dillon had a Doctor of Divinity degree, giving him license to teach Christian theology in Roman Catholic seminaries and universities.
In 1884, Pope Leo XIII, in recognition of Dillon's services to the church, made him a "Monsignor" and gave him the title "Cameriere Segreto" (Secret Waiter).
According to his obituary in The Tablet (issue of 4 February 1893, p. 24) Dillon died on 29 January 1893 in the "Palazzo di Rossi" located in the Piazza d'Aracoeli in Rome, where he had lived for several years after moving to Italy.
He was also critical of the Alta Vendita document, Napoleon Bonaparte's supposed ties with the Masons and the secretive character of the Fenian organisation.