Nuala O'Faolain was born the second eldest in a family of nine children living in the countryside near Dublin. Her father was a well-known Irish journalist under the pen name Terry O'Sullivan; her mother was an avid reader and an alcoholic. Neither parent was much involved in the upbringing of Nuala and her siblings. She managed to obtain an education at University College Dublin, and the University of Hull, and a postgraduate degree from Oxford University. Nuala O'Faolain taught for a time at Morley College, and worked as a television producer for the BBC and Radio Telefís Éireann before becoming a writer.
The New York Times said in her obituary, "Her unblinking, unsentimental description of Irish life in the 1940s and ’50s, and her loveless, impoverished home. . . struck a chord with Irish readers and went on to sell well in Britain and the United States."
In her works, she often discusses her frustration at the sexism and rigidity of gender roles in Catholic Ireland. Her first book "Are You Somebody?" created a sensation when it was published because of her candor about her childhood and her 15-year relationship with the journalist Nell McCafferty. From 2002 until her death, O'Faolain lived much of the time with attorney John Low-Beer and his daughter Anna, splitting her time between Ireland and New York City. In 2012, RTÉ announced a major new documentary on her life.