Todd, James Henthorn (1805–69), librarian and scholar, was born 23 April 1805 at Kildare St., Dublin, eldest son among fifteen children of Charles Hawkes Todd (qv), professor of surgery, RCSI, and his wife Eliza, daughter of Col. Bentley, of the East India Company. He was named for his father's teacher, the surgeon James Henthorn. His younger brother was Robert Bentley Todd (qv), physician. He was first educated at a private day school by the Rev. William Higgin (1793–1867), later bishop of Derry, and graduated BA (1825) from TCD. On the death of his father in 1826 Todd tutored students at TCD and edited the Christian Examiner, a magazine that aimed to put controversy between the established church and the catholic church on a more scholarly footing. In 1831 he was elected FTCD and ordained a deacon in the Church of Ireland. He was ordained priest and graduated MA in 1832. His history of TCD was appended to the university calendar (1833), later revised and printed as an introduction to his List of graduates of TCD (1866). At this time he began contributing essays on Irish church questions, the religious reformer John Wycliffe, and church history to the British Magazine. When the non-denominational national education system was established in Ireland in 1831, Todd believed that the scripture lessons authorised for use were more favourable to catholic than to protestant teaching. He published a letter in Latin, addressed to the English people, purportedly written by the pope to confirm the policy of the national education commissioners. Todd's letter, Sanctissimi domini nostri Gregorii Pap’ XVI . . . (1836) was taken to be a genuine papal document, and caused a good deal of alarm when read at a meeting in Exeter Hall, London, a centre of the evangelical and philanthropic worlds. When Todd revealed himself as the author he was severely criticised, though he defended his actions in a second edition of the same year.
In 1837 he graduated BD at TCD, and was installed as treasurer of St Patrick's cathedral; he received the degree of DD from TCD in 1840. In 1864 he was appointed precentor of St Patrick's. As Donnellan lecturer at TCD (1838–9) he chose as his subject the biblical prophecies regarding the Antichrist, a topic of great interest to many in the contemporary protestant church. Unlike most of his colleagues, Todd rejected the identification of the Antichrist with the pope, and thereby enraged the anti-popery lobby. The lectures were published as Discourses on the prophecies relating to the Antichrist (1840). Todd, with E. R. Quin (qv), Lord Adare, William Monsell (qv), William Sewell (qv), and others, founded St Columba's College in 1843. The school was intended to offer a classical education to the sons of the gentry, as well as the opportunity to learn Irish, for intending clergymen and for those who, as landlords, would be dealing with an Irish-speaking tenantry. Todd's contribution was proportionately greater than that of Sewell, who has had much of the credit for founding the college. It was Todd who found the first premises, organised building works there, campaigned on behalf of the college, lobbied for subscriptions, was sequentially a governor, trustee, fellow, and visitor of the college, and ensured its survival by personally guaranteeing its bank overdraft for several years. He also taught some classes there, and his connection ceased only with his death.
In 1840 he and the Gaelic scholars John O'Donovan (qv) and Eugene O'Curry (qv) founded the Irish Archaeological Society; Todd was its secretary for a time. In TCD he was appointed regius professor of Hebrew (1849) and senior fellow (1850), and held the unsalaried post of assistant librarian from 1831. Realising the existing catalogues were almost useless, he set about the design and construction of a much improved, even ground-breaking, new catalogue. Starting in 1835, the library's roughly 250,000 books were itemised on strips of paper, and in 1846 Todd began to arrange these into publishable form. The first volume went to the printer in 1849, but was not ready until 1864; Todd did not live to see the other volumes in print form, and they were completed by Henry Dix Hutton (1824–1907) in 1887, over fifty years after Todd began work. Todd's remarkable achievement greatly facilitated the use of the library. With help from O'Donovan and O'Curry, he also classified and arranged TCD's important collection of Irish manuscripts. Todd was appointed librarian in TCD in 1852, and managed to increase the library's holdings considerably by judicious purchases.
In 1860 he was given an ad eundem degree at Oxford. One of the most notable scholars of his generation, he was elected MRIA (1833) while still a young man, and contributed over fifty papers to the Academy's Proceedings on ancient Irish manuscripts, antiquities, and artifacts. Elected a member of the RIA council in 1837, he was secretary (1847–55) and president (1856–61). In his inaugural speech as president, he bemoaned the lack of scholarly study of Gaelic but welcomed government support for an Irish–English dictionary. He procured transcriptions and summaries of valuable Irish manuscripts in the Bibliothèque Royale, Brussels, in Rennes and in other European libraries, and gave these to the Academy library. He wrote in Notes and Queries from 1849 until his death. With J. C. Crosthwaite (d. 1874) he edited The book of obits and martyrology of Christ Church, published by the Irish Archaeological Society (1844).
When asked by a London publisher, Todd began to write the lives of the archbishops of Armagh and, although the project failed when the publisher went bankrupt, he managed to complete and publish an exhaustive study of the first bishop in that see, St Patrick, apostle of Ireland (1864), the first modern study of the saint. Todd's portrait of Patrick as an anti-Roman evangelist inspired G. T. Stokes (qv), Thomas Olden, and other protestant writers, at a sensitive time in Irish inter-church relations, to claim the national saint for the Church of Ireland. Todd used somewhat problematic sources such as early Irish saints’ Lives in his argument for the existence of two pre-reformation Irish churches, one imposed at the Norman invasion and supported by the papacy, the other Gaelic in tradition (Welch, 561). With William Reeves (qv), Todd edited the Martyrology of Donegal (1864) by Mícheál Ó Cléirigh (qv), and assisted O'Donovan in his edition of the Irish and English dictionary (1864) of Edward O'Reilly (qv). In 1864 he wrote The book of the Vaudois (1865). Todd's last major work was Cogadh Gaedhel re Gallaibh: The war of the Gaedhil with the Gaill (1867), drawn from two Irish texts (one of which is dated c.1150) and including translations, notes, and genealogies. His sermons and minor works are listed in Cotton's Fasti, ii, 126. He died 28 June 1869 at his residence, Silveracre, Rathfarnham, Co. Dublin; a Celtic cross marks his grave in St Patrick's cathedral cemetery, Dublin; he never married.
Todd was at the centre of academic life in nineteenth-century Ireland; a contemporary (quoted in Webb) called him the sine qua non of every literary enterprise in Dublin. The disposal sale of his library was a major event in the book world; the highest prices commanded to date in Dublin were achieved, and the manuscripts alone made £780; he had owned rarities such as copies of the Book of Lismore, the Book of Clonmacnoise, and a ‘Ritual of St Patrick's cathedral’ (1352). The J. H. Todd lecture series was instituted by the RIA in his memory; the lectures took place and were published irregularly until 1965.