Cahill, Daniel William (1796–1864), catholic priest and public lecturer, was born at Ashfield, in the parish of Arles, Queen's Co. (Laois), on 28 November 1796, the youngest of three sons of Daniel Cahill (1754?–1836), a civil engineer and (it was stated in 1864) a local United Irish leader, by his wife Catherine, daughter of Oliver Brett of Seville. After attending Ferris's Academy, Athy, Co. Kildare, he considered a military career and enrolled as a lay student at Carlow College; but in 1816, owing to the influence of a relation, Michael Corcoran (d. 1819), bishop of Kildare and Leighlin, he moved to Maynooth, where he excelled as a scientist and linguist and became a student at the Dunboyne establishment.
After ordination by Corcoran's successor, James Doyle (qv), he served as curate at Leighlinbridge, Co. Carlow, where his mother's family had lived for 600 years. Obtaining a DD from Rome, he became professor of natural philosophy at Carlow College (1825) and soon proved a successful and popular teacher, counting among his pupils James Fintan Lalor (qv) and Maurice Lenihan (qv). He resigned in 1834 and opened an academy nearby at Erin Lodge, Athy Rd. Soon he moved to Dublin to conduct a school at Seafort House, Williamstown, Co. Dublin (1835–41), and then another school (forerunner of the French College) nearby at Prospect House, Blackrock (1841–6). Though his pupils belonged to well-to-do families, Cahill was a poor manager of finances and seems to have gone bankrupt. About 1847 he apparently became head of another school, Esker College, Athenry, which post he held until 1851. According to Paul Cullen (qv), he was at one time ‘on the verge of being appointed president of one of the queen's colleges, of which he was a supporter’ (Mac Suibhne (ed.), Cullen, iii, 135–6). From 1851, intermittently, his home was Ballyroan Cottage, Rathfarnham, in the diocese of Dublin.
Cahill achieved fame for his preaching and public lecturing. A man of ardent temperament and strong prejudices as well as many talents, he tended to polemics and did not hesitate to attack protestants and Jews as well as British governments of varying hues. He had strong views on slavery, the Irish famine and Napoleon III; he also lectured on scientific subjects, especially astronomy. Helped by his handsome looks and great height, he was a forceful speaker who ‘could transport in ecstasy his listeners to heaven’ (Patrick Cahill's intro. to Letters, 5) and had ‘the power of investing a dry subject with an interest approaching to fascination’ (obit. in Freeman's Jnl). After Cullen became archbishop of Dublin (1852) he banished Cahill from the diocese for preaching without permission. Between 1851 and 1855 Cahill toured England and Scotland, preaching but mainly lecturing on political topics. In December 1859 he went to the USA on another tour. He was praised by the archbishop of New York, John Joseph Hughes (qv), and raised $100,000 for charitable purposes. Daniel Cahill died 28 October 1864 at Carney Hospital, Boston. His embalmed body was deposited in a vault at Holyrood Cemetery and much later, on 9 March 1885, through the efforts of a committee set up by the lord mayor of Dublin, reburied at Glasnevin.
A large number of his writings, which consist chiefly of sermons, lectures and public letters published as tracts or leaflets for popular consumption, are in the RIA. Collections were published in book form in 1856, 1879 and 1888. There are two engraved portraits of Cahill by Harriet Osborne O'Hagan (qv); a statue of Cahill, his right arm raised in preaching, stands in Glasnevin Cemetery. Patrick Cahill (d. 1883), the founder-editor of the Leinster Leader who was imprisoned as a Land Leaguer, and Thomas Cahill (d. 1894), a diocesan priest who later took vows as a Cistercian monk (‘Father Paul’), were nephews.