Iseult was born on 6 August 1894, the daughter of Maud and her then married French Boulangist lover Lucien Millevoye. Maud Gonne claimed that Iseult was conceived in the mausoleum of her late brother, Georges Silvère (1890–1891) who died of meningitis, in an attempt by her parents to reincarnate their dead and still adored infant. Iseult was educated at a Carmelite convent in Laval, France; when she returned to Ireland she was referred to as Maud's niece or cousin rather than daughter.
In 1903 Maud Gonne married John MacBride; Iseult's half-brother Seaghan Sean MacBride was born in 1904 and they separated in 1905. The family lived in France most of the time until John MacBride's death in the 1916 Rising, Mrs MacBride fearing that Sean's father would seize him from her. In a separation settlement MacBride was granted a month's summer custody; he returned to Ireland and never saw his child again. Iseult's relationship with her stepfather was tainted; William Butler Yeats wrote to Lady Gregory in January 1905, the month MacBride and Maud separated, that he had been told MacBride had molested Iseult, who at that time was ten years old.
Iseult was widely considered a great beauty, and temperate and able to speak her mind. She attracted the admiration of literary figures including Ezra Pound, Lennox Robinson and Liam O'Flaherty. Her most famous association was with Yeats, who had long been in love with her mother. In 1916, in his fifties, Yeats wooed and proposed to the 22-year-old Iseult, whom he had known since she was four. She refused, and Yeats became the closest she would have to a father figure.
In 1913, Iseult met Rabindranath Tagore. Inspired by his poetry, she began to learn Bengali in 1914, tutored by Devabrata Mukerjea. Together, in France, they translated some of Tagore's The Gardener into French directly from the Bengali. Tagore left it to Yeats' discretion to decide the merit of the work, but Yeats did not feel sufficiently fluent in French to judge them. The translations were never published.
In 1920, she eloped to London with 17-year-old Irish-Australian Francis Stuart, who would become a respected writer. The couple later married. Their first child, Dolores, died in 1921 of spinal meningitis while three months old. The couple had two other children, Ian and Catherine.
Iseult was not acknowledged as her mother's daughter in Maud Gonne's will when Gonne died in 1953. Iseult died a year later.
- Bolger, Dermot. "A life less ordinary: The tale of Maud Gonne's daughter". The Sunday Business Post, 26 December 2004. Retrieved on 20 June 2007.
- Amanda French, "A Strangely Useless Thing: Iseult Gonne and Yeats," Yeats Eliot Review: A Journal of Criticism and Scholarship 19:2 (2002): 13-24
- Foster, 331-2
- Deirdre Toomey, ‘Stuart , Iseult Lucille Germaine (1894–1954)’, Oxford Dictionary of National Biography, Oxford University Press, 2004
- R. F., Foster. W. B. Yeats: A Life, Vol. I: The Apprentice Mage. New York: Oxford UP, 1997. ISBN 0-19-288085-3.
- Letters to W.B. Yeats and Ezra Pound from Iseult Gonne: A Girl That Knew All Dante Once; Palgrave Macmillan, 2004; ISBN 1-4039-2134-2, ISBN 978-1-4039-2134-5
- Amanda French, "A Strangely Useless Thing: Iseult Gonne and Yeats," Yeats Eliot Review: A Journal of Criticism and Scholarship 19:2 (2002): 13-24.