Ó Muirthile is educated at cork, taking a BA in Irish and French at UCC. His Irish is acquired at school and from sojourns in the Gaeltacht of West Kerry. He is a member of a group of poets at UCC in the late 1960s who choose Irish as a creative medium and are closely associated with the modernist poetry journal Innti, founded by fellow poet Michael Davitt. They are influenced by the work of Cork poet Seán Ó Ríordáin, by the musician and composer Seán Ó Riada, and by popular American culture.
Greg Delanty, writing for Poetry International, claims that a fundamental achievement of Ó Muirthile and other members of the Innti group was to adapt the language to a contemporary urban landscape in a way that reflected the counterculture of the sixties.
Ó Muirthile has been described as a poet of immense formal and musical mastery who reads deeply into the classical and neo-classical poetry of the Irish language. He studies French literature as a student and this influences his work. He translates poetry by Guillaume Apollinaire, François Villon, Jacques Prévert and Anne Hébert.
Ó Muirthile’s first collection of poetry is Tine Chnámh (1984). This receives the Irish American Cultural Institute’s literary award and an Oireachtas prize for poetry. He subsequently publishes a number of other collections. In 1996, he receives the Butler Award for his novel Ar Bhruach na Laoi. Several plays by him have been staged. From 1989 to 2003 he writes a weekly column, “An Peann Coitianta,” for The Irish Times. Poems by him have been translated into English, German, French, Italian, Hungarian and Romanian.
Two of Ó Muirthile‘s poems, Meachán Rudaí and Áthas, have been put to music by the Irish/American group The Gloaming and featured on their third studio album The Gloaming 3.
Mhac an tSaoi is influenced by her stays in the Dingle Peninsula in County Kerry with her uncle, Monsignor De Brún, at his parish of Dún Chaoin. Monsignor de Brún, similarly to his sister, is a distinguished linguist and Celticist, the literary translator of Homer, Dante Alighieri, Sophocles, and Jean Racine into Modern Irish, “and one of the most distinguished literary figures of his time.”
Mhac an tSaoi studies Modern Languages and Celtic Studies at UCD, before going to further research at the Dublin Institute for Advanced Studies and at the University of Paris. She writes the famous work of Christian poetry in Munster Irish, Oíche Nollag (“Christmas Eve”), when she is only 15-years of age.
Mhac an tSaoi spends two years studying in post-war Paris (1945–47) before joining the Irish diplomatic service and is working at the Irish embassy in Madrid when she commits herself to writing poetry in Irish following her discovery of the works of Federico García Lorca.
She remains a prolific poet and is credited, along with Seán Ó Ríordáin and Máirtín Ó Direáin, with reintroducing literary modernism into Irish literature in the Irish language, where it had been dormant since the 1916 execution of Patrick Pearse, in the years and decades following World War II. Her poetry draws on the vernacular spoken by the native Irish speakers of the Munster Gaeltacht of West Kerry during the first half of the twentieth century. Formally, she draws on the song metres of the oral tradition and on older models from the earlier literary tradition. In later work, she explores looser verse forms but continues to draw on the remembered dialect of Dún Chaoin and on a scholarly knowledge of the older literature.
Mhac an tSaoi is elected to Aosdána in 1996 but resigns in 1997 after Francis Stuart is elevated to the position of Saoi. She had voted against Stuart because of his role as an Abwehr spy and in radio propaganda broadcasts from Nazi Germany aimed at neutral Ireland during World War II.
In 2001, she publishes an award-winning novel A Bhean Óg Ón… about the relationship between the 17th-century County Kerry poet and Irish clan chief Piaras Feiritéar and Meg Russell, the woman for whom he composed some of the greatest works of love poetry ever written in the Irish language.
Her poems Jack and An Bhean Óg Ón are both featured on the Leaving Certificate Irish course, at both Higher and Ordinary Levels, from 2006 to 2010. Her literary translation of Rainer Maria Rilke‘s Duino Elegies from Austrian German into the Irish language is published in 2013.
Mhac an tSaoi marries Irish politician, writer, and historian Conor Cruise O’Brien in a Roman Catholic wedding Mass in Dublin in 1962. This makes her the stepmother to O’Brien’s children from his 1939 civil marriage. Her mother is deeply embarrassed by the exposure of the relationship and staunchly opposes the match, as she has long been a close friend of O’Brien’s Presbyterian first wife. Despite their subsequent marriage, the exposure of their extramarital relationship ends Mhac an tSaoi’s diplomatic and civil service career. They later adopted two children, Patrick and Margaret.
She then lives with her husband in New York City, where he becomes a professor at New York University (NYU) after the Congo Crisis destroys O’Brien’s diplomatic career. He is long blamed by the United Nations for the escalation of the Congo Crisis.