Ó Briain, Donnchadh (1897–1981), politician and Gaelic League activist, was born 17 November 1897 in Knockaderry, Co. Limerick, one of two sons and a daughter of David O'Brien of Clonakilty, Co. Cork, creamery manager, and Kathleen O'Brien (née Casey) of Ballyguile. He was educated at Ahalin national school and then at the Redemptorist College at Mount St Alphonsus, Limerick city, but was prevented from going to university by bouts of ill health.
On leaving school he worked in the creamery managed by his father for a number of years. By 1917 he had become involved in the independence movement as a member of Sinn Féin and, later, of the West Limerick brigade of the IRA. He was involved in the republican courts in Limerick and took the anti-treaty side in the civil war. He was deeply involved in the Gaelic League, which he also joined in 1917, having been influenced by Fr Tomás de Bhál (1878–1956). In 1920 Ó Briain was appointed Gaelic League organiser for Co. Limerick, and from 1925 he served in that role for all of Munster province, founding numerous branches of the league. From 1928 to 1932 he served as general secretary of the Gaelic League and also intermittently edited Fáinne an Lae.
A founder member of the Fianna Fáil party in 1926, he stood unsuccessfully in Limerick in the 1932 general election, but was elected as TD for Limerick in 1933, holding his seat in the constituency until 1944. Redrawn boundaries then led to his being elected in West Limerick, which he held from 1944 to 1969. In all, he served from the eighth to the eighteenth dáil without interruption, and throughout his career he invariably spoke to the house in Irish. From 1951 to 1954, and again from 1957 to 1961, he served as parliamentary secretary to the taoiseach and to the minister for defence. He also served the party as chief whip for many years, and died 22 September 1981.
He married (1940) Eileen Liston of Lios an Uisce, a nurse; they kept a farm for a time in Ardgoul, Co. Limerick, but then moved to live in Clouncagh, Co. Limerick. His papers, held in the archives department at UCD, offer a wonderful insight into the life of an ordinary TD working in rural Ireland. They contain details of local election planning, party organisation, public policy, republicanism, and Irish-language issues, but are at their most illuminating when they record representations from constituents.