Máire Mhac an tSaoi (born 4 April 1922) is an Irish language scholar, poet, writer and academic of modern literature in Irish. Along with Seán Ó Ríordáin and Máirtín Ó Direáin she is, in the words of Louis de Paor, "one of a trinity of poets who revolutionised Irish language poetry in the 1940s and 50s."
Mhac an tSaoi was born as Máire MacEntee in Dublin in 1922. Her father, Seán MacEntee, a native of Belfast, was a founding member of Fianna Fáil, a long-serving TD and Tánaiste in the Dáil and a participant in the Easter Rising of 1916. Her mother, County Tipperary-born Margaret Browne (or de Brún), a teacher at Alexandra College, was also an Irish republican. Her uncle, Monsignor Pádraig de Brún, was one of the most respected scholars of the Irish language in the twentieth century. Another uncle was the conservative prelate Michael Cardinal Browne, who was Master of the Dominican Order.
Her late husband was Conor Cruise O'Brien, an Irish politician, writer and historian. The couple were married in 1962 and later adopted two children, Patrick and Margaret.
Mhac an tSaoi has had a lifelong passion for the Irish language and she is today one of the leading authorities on Munster Irish. She is a prolific writer in Irish. She was elected to Aosdána in 1996, but resigned in 1997 after Francis Stuart's elevation to the position of Saoi, which she had opposed because of his allegedly anti-Semitic broadcasts from Nazi Germany during World War II. Her poem Jack and short story An Bhean Óg both have featured on the Leaving Certificate Irish course, at both Higher and Ordinary Levels, from 2006 to 2010.