O'Brien, Ellen Lucy (‘Nelly’) (Ní Bhriain, Neilí) (1864–1925), miniature and landscape artist, and Gaelic League activist, was born 4 June 1864, the eldest of two daughters and one son of Edward William O'Brien, landowner, of Cahirmoyle, Co. Limerick, and Mary O'Brien (née Spring Rice), a sculptor and painter, sister of Thomas Spring Rice, 2nd Baron Monteagle (qv), of Mt. Trenchard, Co. Limerick. Her brother was the artist Dermod O'Brien (qv), and the prominent nationalist William Smith O'Brien (qv) was her grandfather. As a child she spent two years (1866–8) living in the French Riviera with her sick mother until the latter's death from tuberculosis, whereupon she and her siblings were raised by her aunt Charlotte O'Brien (qv), a nationalist and writer. Her father married secondly (1880) Julia Marshall of Yorkshire, by whom he had two sons and two daughters. In 1879 Nelly was sent to school in England, where she later attended the Slade School of Art, London, studying painting.
On her return to Ireland she began to paint miniatures on ivory, using a magnifying glass; she also painted watercolour landscapes. First exhibiting at the RHA in 1896, showing three works including ‘Sketch near Malahide’, she continued exhibiting there intermittently until 1922. In 1895 she was living with her half-brother Conor O'Brien (qv) on Mount St., one of her many Dublin addresses over the years. An early member of the Gaelic League, she was present at its first oireachtas (1897), and founded the Craobh na gCúig gCúigí’ (Branch of the Five Provinces), nicknamed the ‘branch of the five protestants’ owing to its small, but predominantly Church-of-Ireland, membership. In 1904 O'Brien exhibited several portrait miniatures at the London Guildhall exhibition of works by Irish painters. She wrote a long letter defending Douglas Hyde (qv) and the Gaelic League in the Church of Ireland Gazette in 1905. Some of her paintings were shown at the 1906 oireachtas art exhibition at the Technical Schools, Parnell Sq., Dublin; in the same year she became honorary secretary of a newly formed art committee. She included a miniature of William Smith O'Brien among twelve of her works shown at the Munster–Connacht exhibition in Limerick (1906).
In 1907 she was holding meetings of Craobh na gCúig gCúigí every Saturday night in her flat at 7 St Stephen's Green. She founded the Coláiste Eoghain Uí Chomhraí (O'Curry Irish College) in Carrigaholt, Co. Clare (1911). One of her aspirations was to implement a national Irish church between protestants and catholics through the medium of the Irish language. With Seoirse de Rút, she established (1914) the Irish Guild of the Church, an organisation aimed towards the provision of a communal union for members of the Church of Ireland who were dedicated to ‘Irish Ireland’ ideals. As a Gaelic League representative, she travelled to America with Fionán Mac Coluim to collect money and promote Irish industries and art (1914–15). During the 1916 rising, while she was staying with the Hydes at 1 Earlsfort Place, her flat in College Park Chambers was destroyed by gunfire. O'Brien's many portraits included one of Hyde, exhibited at the RHA in 1916. At a mass meeting of women at the Mansion House in 1918, she protested against the bill imposing conscription on Ireland. In 1919 she launched the Gaelic Churchman as the official publication of the Irish Guild of the Church, and in an article, ‘A plea for the Irish services’, pressed her campaign to encourage Irish-language services in protestant churches. As a vice-president of the guild in 1921, she invited Éamon de Valera (qv) to attend one of their meetings.
O'Brien was unmarried. Close friends with the painter Walter Osborne (qv), whom she met through her brother Dermod, she regarded herself as engaged to him, but he died in 1903. Osborne's portrait of her is in the Dublin City Gallery, The Hugh Lane. While visiting Dermod in London, she died suddenly on 1 April 1925 at 66 Elm Park Gardens, and was buried in the family plot at Cahirmoyle.