John Cornelius O'Callaghan (1805 – 24 April 1883) was an Irish historian and writer.

His father was a solicitor from Talbot St. in the city; his mother (née Donovan) came from the south of the country.

[1] He first started writing in the Comet and in the Irish Monthly Magazine of Politics and Literature.

[1] In 1847, at the request of the Irish Archaeological Society, he published Macariae Excidium; The Destruction of Cyprus, or, a Secret History of the War of Revolution in Ireland.

He spent the following years preparing his greatest work, the History of the Irish brigades in the service of France,: From the revolution in Great Britain and Ireland under James II., to the revolution in France under Louis XVI., which was first published in 1867.