O'Callaghan, Edmund Bailey (1797–1880), physician, journalist, and historian, was born 28 February 1797 at Mallow, Co. Cork, youngest among six children of Owen O'Callaghan, a local merchant; nothing is known of his mother. Educated in Dublin, in 1820 he moved to Paris, where he studied medicine for two years. Deciding to emigrate to Canada, he arrived in Quebec in 1823 and continued his medical training; he was licensed to practise in 1827. Obsessed with securing recognition of Ireland's grievances, and support for Irish catholics, he became politically active and was secretary of the Society of the Friends of Ireland (1829–33), president of the Quebec Emigrant Society (1833), and helped found the Irish parish of Quebec. Moving to Montreal, he became editor of the Vindicator and Canadian Advertiser (1833–7). Standing for election to parliament, he was returned for Yamaska county (1834) and became a staunch defender of the national patriotic party, and the key advisor of its leader, Louis-Joseph Papineau.
Becoming increasingly fiery and demagogic, O'Callaghan provoked uproar in 1837 when he used his newspaper to urge the citizens to rebel. A riot broke out in Montreal, and the offices of the Vindicator were ransacked by an angry mob. He was forced to flee Canada after taking part in an abortive insurrection; a warrant was issued for his arrest for treason, and a bounty placed on his head. Settling in the US, he lived (1839–46) in Albany, New York, where he began a medical practice. Retiring from this, he was awarded an MD from St Louis University (1846) and an LLD from St John's College (1856). In 1848 he was invited to become archivist for the state of New York, a position he accepted with great enthusiasm. Over the following twenty-two years he worked tirelessly as the historiographer of the state and published eleven volumes of Documents relative to the colonial history of the state of New York (1853–61), as well as a two-volume History of New Netherlands (1846–8), The register of New Netherland (1865), and other works. Appointed to a similar position for New York City (1870), he edited fifteen volumes of city records, and had eight more ready for press when the Tweed Ring scandal broke; left without any funds to continue, the entire work went unpublished. Retiring to live in New York City, he was confined to his house after an accident in 1877. He died at his home on Lexington Avenue on 29 May 1880 of inflammatory rheumatism and was buried at Calvary cemetery. He married (1830) Charlotte Augustina Crampe, from Ireland. She died in childbirth (1835), and he married secondly (9 May 1841) Ellen Hawke; he had one child from each marriage, but both died in infancy.