Arnold, Thomas (1823–1900), literary scholar and teacher, was born at Laleham, Middlesex, on 30 November 1823, the third child and second son of Dr Thomas Arnold (1795–1842), later famous as the headmaster of Rugby School, and his wife, Mary, née Penrose (1791–1873). Throughout his life he was closely associated with, and often patronised by, his elder brother, Matthew Arnold. Thomas Arnold was educated at Winchester College (1836–7), Rugby School (1837–42), and University College, Oxford (1842–5). On 12 June 1842 he witnessed his father's death from angina.
The young man was noticeably handsome and clever, though hindered by a stammer (sometimes attributed to his father's overbearing character). Arnold's first-class degree in classics (Matthew gained a second) might have enabled him to aspire to a fellowship, but during his studies at Oxford his faith in his father's rationalist, broad-church anglicanism was undermined by David Strauss's Life of Jesus. He developed a vaguely theist form of socialism, influenced by continental Romanticism and by witnessing the poverty of some areas of London. This stage of Arnold's life inspired the character of Philip Hewson in A. H. Clough's narrative poem The bothie of Tober-na-Vuolich. After studying law for a short time at Lincoln's Inn, London, and then working as a clerk at the colonial office, Arnold emigrated to New Zealand in November 1847. A brief and mismanaged experience of farming led him to move to Port Nelson to found a school; this also proved abortive, and in August 1849 he accepted the offer of a post as inspector of schools for Van Dieman's Land (Tasmania), moving to Hobart in early 1850.
On 13 June 1850, Arnold married Julia Sorrell (1826–1888), daughter of the registrar of Van Dieman's Land's supreme court; they had ten children, two of whom died in infancy. Her fierce temper contrasted with his quiet, dreamy nature, and her huguenot ancestry made her determinedly anti-catholic. In 1855 Arnold's persistent scepticism in religious matters gave way to the belief that authority must be found in a living church. He initially returned to anglicanism, then, after reading works by John Henry Newman (qv), embraced catholicism. He was received into the church on 18 January 1856; Julia allegedly threw a brick through the church window.
Anti-catholic sentiment in the colony made Arnold's position untenable; he decided to return to England, and his employers allowed him eighteen months’ leave on half-pay to seek another position. The family reached England in October 1856. Newman appointed Arnold professor of English at the failing Catholic University in Dublin. There followed five years of straitened living in lodgings in Dublin, at Rathmines, and at Kingstown (Dún Laoghaire). This experience, combined with their parents’ quarrels over Julia's improvidence and Arnold's unworldliness, had a devastating effect on the Arnold children. Arnold experienced estrangement from old acquaintances, such as the Whatelys (though his family maintained relations with them), and suffered a degree of culture shock at the ‘ungentlemanly’ behaviour of Irish catholic priests. He was also caught up in continuing tensions as to whether the Catholic University should be Irish or international. Arnold's Dublin lectures formed the basis of A manual of English literature (1862), which saw seven editions in its author's lifetime.
In January 1862 Arnold left Dublin for a somewhat better-paid teaching position at the Oratory school in Birmingham, but tensions with Newman over conditions of employment were accompanied by new religious doubts. From 1859 Arnold wrote for Sir John Acton's the Rambler and its successor, the Home and Foreign Review, which ceased publication in 1864 because of the intensifying conflict between the papacy and continental liberalism. Arnold, a lifelong political liberal (though he combined this outlook with Hellenist and medieval nostalgia and a snobbish disdain for urban commercial civilisation), wondered whether such a church could really be infallible; he was particularly affected by the Mortara case, in which a Jewish child – allegedly clandestinely baptised – was seized from his parents by papal authorities.
In April 1865 Arnold moved to Oxford, where he worked as a private tutor and kept student lodgings; by 1866 he had formally reverted to anglicanism. At Oxford he carried out significant work in medieval and Anglo-Saxon studies: he edited a three-volume selection of the English works of Wycliffe (1869–71), and in 1876 brought out an impressive edition of Beowulf, which coincided with his candidature for the Rawlinson chair of Anglo-Saxon. At the same time he was once again reverting to catholicism. Finding that much of his support came from high-church anglican dons, he felt obliged to announce his reconversion on the eve of the election. His family believed that he wilfully sacrificed the chair and their prospects to religious scruples; Julia wrote to Newman, cursing him. (The victorious candidate was better qualified and strongly supported; Arnold would probably have lost the election anyway.)
Thereafter Arnold lived separately from his wife, though he visited her frequently; they continued to exchange tense letters (not without affection) and he contributed to her support. (At his original conversion it was agreed that their sons would be brought up as catholics and their daughters as protestants; in the event the sons followed him into anglicanism in 1866, and only one reconverted in 1876.) Arnold continued to be active as a scholar, producing editions of medieval texts for the Rolls Series, and also took on work correcting civil service examination scripts.
In April 1882 Arnold was elected a professorial fellow of the RUI; for the rest of his life he lived in Dublin and taught English at University College (run by the Jesuits from 1883). He was pointed out to students (including the young James Joyce (qv)) as a link with Wordsworth and Matthew Arnold. After Julia's death from breast cancer (7 April 1888) he married Josephine Benison (1831–1919) on 9 January 1890. His new bride was a long-standing family friend and intimate correspondent, a zealous Anglo–Irish convert to catholicism from a Co. Cavan landed family. Her influence contributed to his increasingly strict catholicism (he came to feel more sympathy for Paul Cullen (qv) than for Newman) and support for Irish nationalism (he backed home rule and opposed the Boer war, to the dismay of his liberal unionist family).
In his later years Arnold published various works of catholic apologetics (including a catholic dictionary, 1884, compiled with Father W. E. Addis (1844–1917), and a pamphlet on catholic higher education in Ireland, 1897) and scholarly works (significantly Notes on Beowulf, 1898). His autobiography of 1900, Passages in a wandering life, is chiefly of interest for memories of famous acquaintances. He died 12 November 1900 in Dublin of bronchitis and heart failure, and was buried at Glasnevin cemetery on 15 November; a memorial plaque was erected at the university church, St Stephen's Green.
Arnold's eldest daughter, Mary, became a popular novelist under her married name, Mrs Humphry Ward, and the principal financial support of the family (including her father). Her best-regarded novel, Helbeck of Bannisdale (1898) is based on her memories of her parents’ marriage and her ambivalent attitudes to her father and his religion. (He saw the novel before publication and she modified it to take account of his sensibilities.) Another daughter, Julia, was the mother of Julian and Aldous Huxley. Holdings of Thomas Arnold's papers are at Balliol College, Oxford. His lengthy correspondence with his second wife is in private ownership and was used by Bergonzi in the preparation of his biography. Arnold's life reflects many of the tensions of the Victorian mind, family, and society, from which – essentially British – conflicts he escaped to teach aspiring Irish catholic professionals.