MacNeill, Máire (1904–87), folklorist, was born 7 December 1904 at Hazelbrook, Portmarnock, Co. Dublin, fifth child and second daughter of John (Eoin) MacNeill (qv) and Agnes (‘Taddie’) MacNeill (née Moore). After the family moved to 19 Herbert Park in 1908, she started school at the Dominican convent, Muckross Park. Nationalist leaders visited the Herbert Park household. The O'Rahilly (qv) was a neighbour; Roger Casement (qv) was an old family friend. Her older brothers were pupils at St Enda's school, run by Patrick Pearse (qv). Among the Aran women who helped with the children in the bilingual MacNeill household was Maggie Dirrane, heroine of the Robert Flaherty (qv) film Man of Aran (1934).
In 1915 her family went to live with her uncle James McNeill (qv) at Woodtown Park, near Rathfarnham, Co. Dublin. Máire recalled being awakened by the sound of a car coming up the drive on Holy Thursday night in 1916. She slipped out to the stairs and saw Bulmer Hobson (qv) and Ginger O'Connell (qv) coming into the hall to tell her father about the plans for the 1916 rising. After the rising, when her father was sentenced to life imprisonment, MacNeill was sent with her younger sister Róisín to national school teacher Una Folan in Baile na Creige, Inishmore, Co. Galway, on 3 August. The girls attended the national school at Fearann na Coirce until Easter 1917, when they returned to Woodtown Park. She went to Muckross as a boarder in the autumn. The MacNeills moved to Netley, South Hill Avenue, Booterstown, in summer 1918. MacNeill enrolled for a degree in Celtic studies at UCD in 1922; she received her BA in 1925.
From 1927 to 1932 MacNeill worked as a journalist and later as sub-editor of the Cumann na nGaedheal monthly, The Star. She edited the paper from September 1931 until the spring of 1932, when the Star was replaced by the weekly United Ireland. She served as sub-editor until she left to assist her father with his memoirs. With her sister Róisin, she illustrated Finnsgéalta ó India (1932) by Josephine McNeill (qv).
In 1935 Séamus Ó Duilearga (qv) invited MacNeill to be the office manager of the newly founded Irish Folklore Commission. After training in Swedish folklore methods at Uppsala University, MacNeill joined Seán Ó Súilleabháin (qv), as a commission archivist and began research for The festival of Lughnasa (1962, 1983), her magisterial study of the Irish harvest festival. Using oral tradition, including the responses to her 1942 questionnaire about harvest customs, other narratives in the archives of the Irish Folklore Commission, archaeological and historical evidence, and Old Irish literary sources, MacNeill examined the 195 sites associated with Lughnasa gatherings, the most famous of which is the annual pilgrimage on the last Sunday of July to Croagh Patrick, Co. Mayo. She discovered survivals of the old festival and traced them in nineteenth- and twentieth-century narratives and customs which document the way that Christian practices became syncretised with the sites’ earlier pagan customs. MacNeill was awarded a D.Litt. for Lughnasa by the NUI in 1964. The festival of Lughnasa's documentation of the close coexistence of Celtic and Christian traditions in the Irish countryside – as well as the Lughnasa survivals: hill gatherings, berry picking, and especially dancing – influenced Brian Friel's play ‘Dancing at Lughnasa’ (1990).
MacNeill left the Irish Folklore Commission in 1949 when she moved to Boston. A visiting lecturer in Irish folklore at Harvard University (1964, 1965), she helped train the first generation of American graduate students in Celtic studies. After she settled in Ireland in 1967, she translated two folklore classics into English: Siscéalta ó Thír Chonaill: fairy legends from Donegal (1977), the collection by Seán Ó hEochaidh (qv) of Donegal fairy legends, edited by Séamus Ó Catháin; and Seán Ó Conaill's book: stories and translations from Iveragh (1981), Séamus Ó Duilearga's Kerry collection Leabhar Sheáin I Chonaill (1948).
Having settled in north Clare, MacNeill explored the region's folklore in her last work, Máire Rua: lady of Leamaneh. Published posthumously in 1990, the study compares the tradition surrounding Máire Rua with the facts of her life preserved in O'Brien family records, particularly those in The Inchiquin manuscripts (1961). MacNeill separated the versions of the ‘sovereign goddess’ myth from the historical Máire Rua to reveal a shrewd businesswoman who protected her heirs' property interests during the political and religious turmoil of the seventeenth century.
MacNeill married (1949) John L. Sweeney, American poet and curator of the poetry room at Harvard's Lamont Library. She died at her home, Poulivan, Corofin, Co. Clare, on 15 May 1987. She bequeathed the Sweeney collection of fourteen paintings and drawings, including ‘Still-life with a mandolin’ by Pablo Picasso, ‘Pierrot’ by Juan Gris, and ‘The singing horseman’ by Jack B. Yeats (qv), to the NGI in memory of John L. Sweeney.