His father's family was Old English Irish and descended from Sir Henry Dillon who came to Ireland with Prince John in 1185.

[6] He devoted himself less to the spiritual direction of his diocese than to the temporal welfare of its inhabitants, carrying out many works of public utility, bridges, canals, roads, harbours, etc.

Soon afterwards both went to London, where he was visited in 1797 at his home in Thayer Street, Marylebone, by Henriette-Lucy, Marquise de La Tour du Pin Gouvernet.

[9] On 15 July 1801, at Paris, Napoleon and Pope Pius VII signed the Concordat of 1801 and most of the French clergy that had gone into exile or hiding returned to take up again their normal duties.

Dillon however disobeyed the pope and rejected the Concordat, probably because it suppressed his see at Narbonne, or because he wanted to avoid paying his debts in France.

He was buried in St Pancras churchyard, which was the burial place favoured by the émigré community, as there was no official Catholic cemetery available.

Between March 2002 and June 2003, part of the St Pancras Old Church graveyard was excavated[13] in preparation for the London terminus of the Channel Tunnel Rail Link.