Gilbert, Sir John Thomas (1829–98), merchant, historian, archivist, and librarian, was born 23 January 1829 at 23 Jervis St., Dublin, second son and fifth child of John Gilbert (1791–1833), wine and cider importer and Portuguese consul, and Mary Anne Gilbert (née Costello), both of Dublin. Gilbert's grandfather, Henry Gilbert, had emigrated to Ireland from Devon in the 1780s, when he established a firm to import Gilbert's Devonshire cider into Ireland. Henry's son John carried on the family business, importing cider from Devon and wines from the Continent. John Gilbert died in 1833 and his widow took over the management of the family business. Mary Anne Costello's father was a coachmaker, Philip Costello, who was based at the Jervis St. premises later owned by John Gilbert.
The Gilbert children were baptised and brought up as catholics, Mary Anne Gilbert's religion. Thus, John Thomas was educated at St Vincent's seminary, Usher's Quay, at Bective College, and later at Prior Park College, Bath. His mother refused to allow him to enter the University of Dublin, so at 17 he joined the family business, which was by then being run by Mary Anne and her eldest son, Henry Costello Gilbert. John Thomas was involved with the importation business until the late 1860s, when he sold his interest.
Gilbert's life work was the recording of history; from an early age he had read historical works and documents, and he won a silver medal in history at Prior Park. He read in Marsh's Library and the RDS library. In 1848 he joined the Celtic Society (this later amalgamated with the Irish Archaeological Society to become the Irish Archaeological & Celtic Society), becoming its secretary in 1852. The Society aimed to publish original documents illustrative of Irish history, with translations and notes. Scholars such as John O'Donovan (qv) and James Henthorn Todd (qv) were members and edited and published, under its aegis, hitherto inaccessible works. In 1851 Gilbert was a founder member of the Irish Quarterly Review, of which he became editor, and to which he contributed numerous articles and reviews, including a series entitled ‘The streets of Dublin’ (March 1852–December 1853), which formed the basis of The history of the city of Dublin (1854–9), and earned him the RIA's Cunningham gold medal in 1862. This magisterial publication quickly became the definitive work on Dublin and helped to establish Gilbert as a scholar and historian. In April 1852 Gilbert had been put forward, unsuccessfully, for election to the RIA, but on 9 April 1855, a year after the publication of the first volume of The history. . ., he was elected on the proposal of James Henthorn Todd, William Wilde (qv), George Petrie (qv), Charles Haliday (qv), and Thomas Larcom (qv), among others, all leading antiquarians and scholars of the day.
Gilbert was elected to the academy council in 1856, serving on the committee of antiquities (1856–70) and the merged committee of polite literature and antiquities from 1870 until his death. He became librarian to the academy in 1861, a post he held for the remainder of his life, with the exception of two periods (1876–8, 1887–8). As librarian, Gilbert was responsible for organising the collections and for having them catalogued, and he personally arranged and catalogued the important Haliday pamphlet collection. However, Gilbert's relations with the academy were not without incident. He had successfully supervised the academy's publication of Leabhar na hUidhri (1870) and Leabhar Breac (1876), but owing to a mental breakdown suffered by Gilbert in 1874 Robert Atkinson (qv) had been elected librarian in 1876 and charged with the editorship of the Book of Leinster. Atkinson continued to discharge this function after Gilbert's resumption of office in 1878. Gilbert insisted that he should be given control of the publication, but the academy stood firm and Atkinson was credited with editorship of the work.
Another debacle occurred over the allocation of the Todd memorial fund. Although it had been agreed that the fund should be used to endow a professorship of Celtic languages in memory of James Henthorn Todd, Gilbert invested it in government stock. Without consulting the academy council, he transferred the investment to the court of chancery, swearing an affidavit that the sum should be used to ‘produce a photographic reproduction of the Book of Lecan as a memorial to Todd’. The effect of this action was that Sir Samuel Ferguson (qv), Academy president, ensured that the Todd professorship was established in December 1879.
Gilbert's disputes with the academy were minor in comparison with his criticisms of the Irish Record Office. As early as 1854 he had highlighted the need for the systematic publication of the Irish records, as well as the pressing need to arrange and catalogue them. In 1859 the Commission into Chancery Offices (Ireland) reported on the unhealthy state of the Irish records and was scathing of the work being carried out on them. A process of reorganisation was begun with the purchase of a site adjacent to the Four Courts in Dublin, intended to house the courts’ records, but not those of the administration. Gilbert had pressed above all for the publication of the records, and this was set in train with the publication of volume I of the Calendars of the patent & close rolls of Ireland. A second building project to house the public record office was initiated, and Gilbert campaigned at every level to ensure that all the records would be centralised there. However, his vituperative style and his drawing attention to the incompetence of the rolls office staff, their lack of archival method, and inaccurately edited calendars, earned him many enemies. Especially damning was the series of pamphlets written by Gilbert in 1863–4 under the titles Record revelations and On the history, position and treatment of the public records of Ireland, by ‘An Irish archivist’. Eventually, Gilbert's arguments prevailed and the office was centralised, but his ambition to become deputy keeper of the records office was not realised. Sir Samuel Ferguson was judged to be a safer bet, while J. J. Digges La Touche was appointed assistant deputy keeper, and Gilbert secretary. Apart from the imposition of an intermediate post in the staff structure, the organisation of the records was accorded precedence over publication; Gilbert was thoroughly marginalised. In 1869 he was appointed inspector in Ireland of the Royal Commission on Historical Manuscripts. The secretaryship of the records office was abolished by a treasury commission in 1875 and Gilbert was compelled to leave the office. He suffered a mental breakdown and was looked after by his sister Mary until his recovery in 1877.
Gilbert had a happier association with Dublin corporation, which in 1865 had requested him to inspect and advise on its muniments. In 1866 he presented a report that formed the basis for a programme of classification and conservation, which he supervised. He published some of the muniments as Historic and municipal documents of Ireland, A.D. 1172–1320, from the archives of the city of Dublin (1870).
Throughout his career Gilbert published copiously: works include a History of the viceroys of Ireland . . . (1865), A contemporary history of affairs in Ireland from 1641 to 1652 . . . (3 vols, 1879–80), History of the Irish Confederation . . . (7 vols, 1882–91), and Calendar of the ancient records of Dublin in the possession of the municipal corporation of that city . . . (7 vols, 1889–98), the last continued by his widow Rosa Mulholland (qv), Lady Gilbert, in twelve further volumes (1901–22). More recent scholarship has shown that this last publication contains errors and omissions.
Gilbert, his mother, and sisters moved from Jervis St. to Villa Nova, Blackrock, Co. Dublin, in 1854. Mary Anne died in 1870 and his last sister, Mary, in 1886. In 1891 he married the novelist Rosa Mulholland, daughter of Dr Joseph Stevenson Mulholland of Belfast. Gilbert was awarded an honorary LLD by the RUI in 1892 and received a knighthood in 1897. He died 23 May 1898 of heart failure on his way to an academy meeting.
Gilbert amassed a fine library, which was purchased by Dublin corporation on his death. The Gilbert Library is housed in the Dublin City Library and Archive, Pearse St., Dublin. Gilbert's papers are held by the NLI, Dublin City Library and Archive, and the RIA. Other correspondence is held in a wide range of collections (see R. J. Hayes (ed.), Manuscript sources for the history of Irish civilisation, ii: persons (1965), 267–8). Gilbert's publications are listed in Máire Kennedy, ‘Contribution towards a bibliography of the writings of John T. Gilbert’ in Clark and others (ed.), Sir John T. Gilbert 1829–1898 . . . (1999), 141–7. Two framed photographs were bequeathed to the RIA by Lady Gilbert in 1922; these show Gilbert as a young man and in old age. Both are by Alexander Bassano (1829–1913), of the Bassano Studios, London, who made photographic portraits of many distinguished persons in Victorian and Edwardian Britain. The photograph of Gilbert in old age is also held by the National Portrait Gallery, London. A portrait of Gilbert by Sir John Lavery (qv), inscribed ‘John Thomas Gilbert, antiquarian (1829–97 [sic])’ and dated 1910, was presented to the NGI by Lady Gilbert in 1912. It is recorded, and a monochrome copy of it is reproduced, in the NGI's National Gallery of Ireland: illustrated summary catalogue of paintings (1981), 260.