Ó Dónaill, Niall (1908–95), writer and lexicographer, was born 27 August 1908 in Ailt an Eidhinn near Loch an Iúir, Co. Donegal, the eldest of six children of a farmer, Tarlach Ó Dónaill, and his wife, Éilís Nic Ruairí. His mother was a musician and a storyteller and for many years his father spent the months of June to November working for a farmer near Motherwell, Scotland. He received his early education in the local school in Loch an Iúir. Afterwards, he obtained a two-year scholarship to Coláiste Adhamhnáin in Letterkenny and a county council scholarship to UCD where he studied English, history and Irish under Douglas Hyde (qv) and Osborn Bergin (qv) in the Irish department, although he did not rate their teaching skills very highly. He spent his summers as a student teaching in Fr Ó Muirí's Irish summer college in Rinnafarset, Co. Donegal. Due to his late arrival back from Donegal at the end of the summer, he failed to sit his final year exams and left UCD without a degree. On leaving college he spent a year teaching in the CBS, Cashel, Co. Tipperary.
By 1927 he was contributing essays, stories and poems to An tUltach and from 1929 was working full time as a translator for An Gúm publishing company, translating novels by authors such as Padraic Colum (qv), Walter Scott, R. L. Stevenson, H. Rider Haggard, and Jack London from English into Irish. The author Seosamh Mac Grianna (qv) also worked there at the time and both men regularly competed on their weekly totals of words translated. During one week in particular, Ó Dónaill translated 27,000 words of Talisman compared to Mac Griana's 29,000 of Ivanhoe. In total, thirteen of his translations were published: Scairt an dúthchais (1932); Ise (1933); Máire (1935); Cineadh an fhásaigh (1935); Mac rí na hÉireann (1935); An chloch órtha (1936); Roibeart Emmet (1936); An Ministir Ó Ceallaigh (1937); Commando (1938); Seachrán na naingeal (1946); An tollphéist (1939); Maighistir Bhaile na Trágha (1938). He also translated a work by H. B. Zimmerman entitled Dhá choinneal do Mhuire (1958). ‘An bealach chun na róimhe’ has been attributed to Ó Dónaill but it does not appear to have been published. He also translated a work on Belfast by Denis Ireland (qv) for the Sáirseal agus Dill publishing company, but it too was never published. Ó Dónaill believed that so much translating set him back seven years as a creative writer, and he and other employees of An Gúm were very critical of its concentration on translation claiming that it suppressed the development of writing in Irish.
Ó Dónaill married Sorcha Ní Ghallchóir from the Rosses in Co. Donegal in 1930 and they had five children, including a daughter who died when she was five. The same year he was appointed assistant editor to Lambert Mac Cionnaith on the Foclóir béarla agus gaedhilge (1935). He spent two years working on the project but lost his job due to state cutbacks. This brought financial hardship to the Ó Dónaill family. He was forced to sell the new house he had just bought and Sorcha and their two children returned to Donegal. Ó Dónaill remained in Dublin sharing an apartment with his friend Séamas Ó Grianna (qv). He was re-employed on the dictionary project when the Department of Finance provided money for its publication. He joined the civil service in 1935 having won first place in the entrance exam and worked in the Department of Industry and Commerce and then the Department of Social Welfare. In Dublin in 1952 he became manager of the Werburgh Street employment exchange.
Ó Dónaill continued to write throughout this period, and his collection of short stories dealing mainly with the harshness of his life growing up in Donegal was published as Bruighean feille (1934). His life of John Mitchel (qv) appeared under the title Beatha Sheáin Mistéil (1937). Ó Dónaill greatly admired Mitchel as a brave and steadfast opponent of British rule in Ireland, and went to some lengths to defend his support for slavery during his exile in the USA. He also edited a number of works including Seanchas na Féinne (1942–3) and Scéalta Johnny Shéimisín (1948) for Comhaltas Uladh. His pioneering work Forbairt na Gaeilge (1951) studied the role of dialects in the development of a standard written Irish and argued that the Irish language's salvation would only take place in Dublin. This work was considered revolutionary by Ó Dónaill himself and published at a time when the majority of Ulster Irish language writers were against standardisation. Another publication the following year, Na glúnta Rosannacha (1952), was a celebration of his native Rosses. He also contributed numerous articles to the Donegal Annual.
In 1959 Ó Dónaill was appointed editor of Foclóir Gaeilge–Béarla and worked on the project together with Tomás de Bhaldraithe (qv) as advisory editor until 1977. During the 1960s Ó Dónaill took part in a weekly radio programme, Fadhbanna Gaeilge with other Irish language experts such as de Bhaldraithe, Máirtín Ó Cadhain (qv) and Donncha Ó Cróinín. Together with Pádraig Ó Maoileoin, he published five specialised dictionaries in Irish. Before his death he completed a new edition of Graiméar Gaeilge na mBráithre Críostaí as well as a modern Irish version of Táin bó Cuailgne.
Ó Dónaill won an oireachtas award in 1980 and TCD conferred him with an honorary D.Litt. in June 1982 for his contribution to the Irish language. He survived his wife by just one month and died 10 February 1995. Ó Dónaill is interred in Glasnevin cemetery.