From A Compendium of Irish Biography, 1878
Brennan, John, M.D., born at Ballahide, County of Carlow, about 1768. He was educated to the medical profession, and obtained a wide reputation for his successful practice in puerperal disorders. An excellent classical scholar, a man of talent and humour, his sallies were long remembered. As editor of the Milesian Magazine he unhappily prostituted his talents, by ridiculing for pay the Catholic leaders of his day, and abusing the members of his own profession. He died in Dublin, 29th July 1830, aged 61. In Notes and Queries, 3rd Series, will be found reference to a copy of the Milesian Magazine in the British Museum, containing a MS. key to Brennan's pseudonyms.Sources
39. Biographical Dictionary, Imperial: Edited by John F. Waller. 3 vols. London, N.D.
254. Notes and Queries. London, 1850-'78.
O'Callaghan, John C., see No. 186.