She was educated at University College Dublin, Sapienza University of Rome and the Sorbonne Paris. She has worked as a writer, language teacher, editor and translator and has lived in France, Italy, and the USA. Her novels include Godded and Codded (1970), Women In The Wall (1975), No Country for Young Men (1980), The Obedient Wife (1982), The Irish Signorina (1984), The Judas Cloth (1992) and Adam Gould (2009). Her short story collections include We Might See Sights! (1968), Man in the Cellar (1974), Melancholy Baby (1978) and Daughters of Passion (1982). As Julia Martines, she translated Two Memoirs of Renaissance Florence: The Diaries of Buonaccorso Pitti and Gregorio Dati and Piero Chiara's A Man of Parts. Her No Country for Young Men was shortlisted for the 1980 Booker Prize.
She lives in Los Angeles where she is married to historian of the Renaissance, Lauro Martines. They have one son. With her husband she co-edited Not in God's Image: Women in History from the Greeks to the Victorians (1973)
O'Faolain writes about women's roles in society, power, faith and sexuality, and about Irish dilemmas of female identity. "Women in the Wall" (1975) is a history of Saint Radegund, who in the sixth century founded a monastery in Gaul. With her husband, O'Faolain edited Not in God's Image: Women in History from the Greeks to the Victorians (1973), and has just produced a new novel, Adam Gould, which is set in a lunatic asylum. Although it's her first book in 17 years, it explores familiar themes: clerical intrigue, family history and farce, with madness added to the mix. 'I like fiction to be a Trojan horse, she says. 'It can seem to be engineering an escape from alien realities, but its true aim is to slip inside them and get their measure.