Born as Ann Teresa O'Donnell in Guildford, Surrey, UK in 1939, Keane studied medicine at Trinity College, Dublin. She dropped out without taking a degree and later married a young barrister, Ronan Keane. The couple separated in the 1990s, and Ronan Keane went on to become Chief Justice.
She was the principal contributor of the Sunday Independent’s long-running gossip column, The Keane Edge. In the column there were often hints of a relationship with a prominent political figure, named in the column as Sweetie, and her relationship was widely known in certain circles, though never openly confirmed. She spent the majority of her career working for the Irish newspaper the Sunday Independent. She later left the paper on bad terms after selling the story of her 27-year affair with former Taoiseach Charles Haughey to the British newspaper The Sunday Times, a rival to the affiliated London Independent newspapers, though she admitted her affair on The Late Late Show in 1999.
Keane died on 1 June 2008 after a long illness. She is survived by her children Jane, Madeleine and Justine. Her son Tim died in 2004.