Marian Keyes est née le 10 septembre 1963 à Limerick, dans l’ouest irlandais elle grandit à Dublin. Elle étudie le droit à l’Université du Dublin. Elle vit à Londres plusieurs années. À l’âge de 30 ans, après de nombreuses dépressions et problèmes avec l’alcool elle commence à écrire.

C’est alors qu’elle envoie ses articles à une maison d’édition. Son premier roman Watermelon est publié en 1995. Depuis, elle n’a pas cessé d’écrire avec son style particulier, connu comme « chick lit ». Dans l’actualité, elle habite à Dún Laoghaire avec son mari, Tony.

Marian Keyes est connue comme l’une des fondatrices du « chick lit ». C’est un style écrit pour jeunes femmes et qui parle des sujets d’actualité avec un point de vue féministe et encourageant. Il combine la comédie avec des sujets comme l’infidélité, le divorce, l’addiction, ou la violence de genre. L’écriture de Marian Keyes montre des jeunes filles qui vivent un moment difficile dans leur vie mais qui le surmontent.

Born in Limerick and raised in Monkstown, Keyes earned a law degree from Dublin University, but immediately disregarded it, left Ireland and became a waitress in London, feeling as though she did not deserve a well-paid career. Keyes began composing short stories after she found work in an accounts office, but initially had no intention of completing a novel, arguing that it would take too long.
In this period of her life, she underwent a severe struggle with alcoholism, but overcame this in 1995 at a rehabilitation center in Dublin, Ireland.
However, following a letter back from the publisher whom she'd sent her manuscripts to, she began work on a book, and thus her first feature-length story, Watermelon, was born. Known for her self-deprecation, Keyes often says that she "became a writer by accident".

Although many of her novels are known as comedies, they are often filled with dark themes including domestic violence, drug abuse, mental illness, divorce and alcoholism, most of which are loosely based on her own life experiences.
She is regarded by her fans as a pioneer of the so-called 'chick-lit' genre; her stories usually revolve around a strong female character who overcomes numerous obstacles to achieve lasting happiness.

Marian Keyes is one of the most successful Irish novelists of all time. Though she was brought up in a home where a lot of oral story-telling went on, it never occurred to her that she could write. Instead she studied law and accountancy and finally started writing short stories in 1993 “out of the blue.” Though she had no intention of ever writing a novel (“It would take too long”) she sent her short stories to a publisher, with a letter saying she’d started work on a novel. The publishers replied, asking to see the novel, and once her panic had subsided, she began to write what subsequently became her first book Watermelon.

It was published in Ireland in 1995, where it was an immediate, runaway success. Its chatty conversational style and whimsical Irish humour appealed to all age groups, and this appeal spread to Britain when Watermelon was picked as a Fresh Talent book. Other countries followed (most notably the US in 1997) and Marian is now published in thirty-three languages.

To date, the woman who said she’d never write a novel has published ten of them: Watermelon, Lucy Sullivan is Getting Married, Rachel's Holiday, Last Chance Saloon, Sushi for Beginners, Angels, The Other Side of the Story, Anybody Out There and This Charming Man, all bestsellers around the world, a total of twenty-three milllion of her books having been sold to date. The Other Side of the Story sold over half a million copies in paperback, making it the second highest selling paperback novel published in 2005, with Anybody Out There repeating the feat in 2007, and This Charming Man set to surpass it in 2009.

Anybody Out There won the British Book Awards award for popular fiction and the inaugaral Melissa Nathan prize for Comedy Romance. This Charming Man won the Irish Book award for popular fiction.

The books deal variously with modern ailments, including addiction, depression, domestic violence, the glass ceiling and serious illness, but always written with compassion, humour and hope.

Her work has come to the attention of Hollywood; Rachel’s Holiday will be filmed next year. Lucy Sullivan is Getting Married has been made into a sixteen part television series, Watermelon was a made for TV movie in 2003, and Last Chance Saloon was filmed in French – Au Secours J’ai Trente Ans was released in 2004.

As well as novels she writes short stories, and articles for various magazines and other publications. She is also involved with various charities – she contributed to a multi-authored book, Yeats is Dead! where all the royalties were donated to Amnesty International. She has published two collections of her journalism, titled Under the Duvet and Further Under the Duvet, and donated all royalties from Irish sales to the Simon Community, a charity which works with the homeless.

She was born in Limerick in 1963, and brought up in Cavan, Cork, Galway and Dublin; she spent her twenties in London, but is now living in Dún Laoghaire with her husband Tony. She includes among her hobbies, reading, movies, shoes, handbags and feminism.