Colm Tóibín was born in Enniscorthy, County Wexford in the southeast of Ireland in 1955.He was the second youngest of five children. His grandfather, Patrick Tobin, was a member of the IRA, as was his grand-uncle Michael Tobin. Patrick Tobin took part in the 1916 Rebellion in Enniscorthy and was subsequently interned in Frongoch in Wales. Colm Tóibín's father was a teacher who was involved in the Fianna Fáil party in Enniscorthy. He received his secondary education at St Peter's College, Wexford, where he was a boarder between 1970 and 1972. He progressed to University College Dublin, and graduated in 1975. Immediately after graduation, he left for Barcelona. Tóibín's first novel, 1990's The South, was partly inspired by his time in Barcelona; as was, more directly, his non-fiction Homage to Barcelona (1990). Having returned to Ireland in 1978, he began to study for a masters degree. However, he did not submit his thesis and left academia, at least partly, for a career in journalism.

The early 1980s were an especially bright period in Irish journalism, and the heyday for the monthly news magazine Magill. Tóibín became the magazine's editor in 1982, and remained in the position until 1985. He left due to ongoing differences with the managing director Vincent Browne.

The Heather Blazing (1992), his second novel, was followed by The Story of the Night (1996) and The Blackwater Lightship (1999). His fifth novel, The Master (2004), is a fictional account of portions in the life of author Henry James. He is the author of other non-fiction books: A Walk Along the Irish Border (1994), (reprinted from the 1987 original edition) and Travels in Catholic Europe (1994).

He has written a play that was staged in Dublin in August 2004, Beauty in a Broken Place. He has continued to work as a journalist, both in Ireland and abroad, writing for the London Review of Books among others. He has also achieved a reputation as a literary critic: he has edited a book on Paul Durcan, The Kilfenora Teaboy (1997); The Penguin Book of Irish Fiction (1999); and has written The Modern Library: The 200 Best Novels in English since 1950 (1999), with Carmen Callil; a collection of essays, Gay lives from Wilde to Almodóvar (2002); and a study on Lady Gregory, Lady Gregory's Toothbrush (2002).

Tóibín is a member of Aosdána and has been visiting professor at Stanford University, The University of Texas at Austin and Princeton University. He has also lectured at several other universities, including Boston College, New York University, Loyola University Maryland, and The College of the Holy Cross. In 2008, he received the honorary degree of Doctor of Letters (DLitt) at the University of Ulster in recognition of his contribution to contemporary Irish Literature. In January 2010, he was named the winner of the Costa Novel Award for his novel Brooklyn.

Tóibín has written two short story collections. His first, Mothers and Sons explored, as the name suggests, the relationship between mothers and their sons and was published in 2006 and was reviewed favourably (including by Pico Iyer in The New York Times). His second, broader collection, The Empty Family is to be published in 2011.

Tóibín is a judge for the 2011 Griffin Poetry Prize.

Tóibín's work explores several main lines: the depiction of Irish society, living abroad, the process of creativity and the preservation of a personal identity, focusing especially on homosexual identities ... Tóibín is openly gay ... but also on identity in front of loss. The "Wexford" novels, The Heather Blazing and The Blackwater Lightship, use the town of Enniscorthy where he was born as narrative material, together with the history of Ireland and the death of his father. An autobiographical account and reflection on this episode can be found in the non-fiction book, The Sign of the Cross. In 2009 he published Brooklyn, a tale of a woman emigrating to Brooklyn from Enniscorthy.

Two other novels, The Story of the Night and The Master revolve around characters who have to deal with a homosexual identity and take place outside Ireland for the most part, with a character having to cope with living abroad. His first novel, The South, seems to have ingredients of both lines of work. It can be read together with The Heather Blazing as a diptych of Protestant and Catholic heritages in County Wexford, or it can be grouped with the "living abroad" novels. A third topic that link The South and The Heather Blazing is that of creation. Of painting in the first case and of the careful wording of a judge's verdict in the second. This third thematic line culminated in The Master, a study on identity, precedeed by a non-fiction book in the same subject, Love in A Dark Time. The book of short stories "Mothers and Sons" deal with family themes, both in Ireland and Catalonia, and homosexuality.

His hero is Jack Yeats.