Mulcahy, Denis Dowling (1840–1900), Fenian, was born near Clonmel, Co. Tipperary, son of Denis Mulcahy, a farmer of Redmondstown, Co. Tipperary, who sympathised with the Young Ireland rising of 1848 and ten years later offered support to the Fenian leader, James Stephens (qv). His son continued these political activities; John O'Leary (qv) credits him with stirring up strong Fenian sentiments among the farmer class in Tipperary. He went to Dublin about 1863 to study medicine and to take on the sub-editorship of the Fenian paper, the Irish People. On 15 September 1865 the offices of the paper were raided and Mulcahy was arrested, along with John O'Leary, Thomas Luby (qv), and Jeremiah O'Donovan Rossa (qv). Sentenced (20 January 1866) to ten years' penal servitude for treason-felony, he was sent initially to Pentonville and then transferred to Portland. Certified for hard labour, he fell ill and was diagnosed with haemoptysis, or haemorrhaging of the lungs, but was nevertheless kept at hard labour when he was transferred to Dartmoor prison (winter 1867). After three weeks he began haemorrhaging anew and was finally sent to Woking invalid prison. He did not serve his full sentence, as in December 1870 Fenian prisoners were granted amnesty on condition of expatriation from the UK for the term of their original sentences. A plea of mitigation from exile on the grounds that he was the sole support of an aged, decrepit father was unsuccessful, and Mulcahy sailed to New York on the SS Russia (January 1871) with eight other released Fenians. During his incarceration, his fiancée, a Miss Power from Tipperary, married the Fenian (and later informer) Gen. F. F. Millen (qv).
In New York Mulcahy helped form a directory of Irish political exiles, which aimed to unite all Irish nationalist groups in America into one organisation. He returned to England in June 1876, when his term of exile was up, to give a lecture in London on national independence for Ireland, but he otherwise settled in America. On 6 February 1877 he found the former head of the American Fenian Brotherhood, John O'Mahony (qv), dying in a New York garret and, though he ministered to him, was unable to save his life. He accompanied the body to Ireland, where it was brought from Queenstown (Cobh), Co. Cork, to Dublin and given an enormous funeral before burial in Glasnevin. Writing about the event for the Nation, Mulcahy concluded sharply that ‘we seem to set more value on the dead patriot's bones than on his living brains’ (3 Mar. 1877). Bringing O'Mahony's remains to Ireland involved Mulcahy in a bitter dispute with the IRB leadership; he had apparently been promised by O'Donovan Rossa $1,000 from the Fenian's skirmishing fund to defray expenses, but was only ever paid $537. He sued the trustees of the skirmishing fund, who held that they could not be held responsible for Rossa's promises; he lost his case in January 1884 but continued trying to drag it through the courts. John Devoy (qv) therefore considered him a fool, but John O'Leary continued to regard him with great affection. Mulcahy was a nominal member of Clan na Gael during the 1880s. He opposed the ‘new departure’ alliance of Fenians, constitutionalists and agrarian activists, and was contemptuous of Parnell (qv), believing him to have dictatorial ambitions. He continued to correspond with O'Leary and C. G. Doran (qv) during the 1880s and 1890s, criticising the former for his tolerance of the Irish party after 1885, and staying occasionally at the latter's home in Queenstown in the late 1890s. His last years were spent in prosperity; he built up a good medical practice in Newark, New Jersey and devoted his spare time to compiling an Irish biographical dictionary, which was never, however, published, nor was his research retained. He died in Newark on 13 September 1900 and his large library of 20,000 volumes, worth about $10,000, was sold by auction.