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 Iseult’s 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 Sean MacBride was born in 1904 and the couple separated in 1905. The family lived in France most of the time until John MacBride’s death in the 1916 Rising, with Gonne fearing that Sean’s father would seize him from her. In a separation settlement, MacBride was granted a month’s summer custody, however, he returned to Ireland and never saw his child again. Iseult’s relationship with her stepfather was tainted by an allegation by William Butler Yeats, who 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. However, many critics have suggested that Yeats may have fabricated the event due to his hatred of MacBride over Maud’s rejection of him in favour of MacBride. The divorce papers submitted by Gonne made no mention of any such incident – the only charge against MacBride that was substantiated in court was that he was drunk on one occasion during the marriage and Iseult’s own writings make no mention of the allegation.
Iseult was widely considered a great beauty, and temperate, able to speak her mind. She attracted the admiration of literary figures including Ezra Pound, Lennox Robinson and Liam O’Flaherty. Her most infamous association was with Yeats, who had long been in love with her mother. In 1916, in his fifties, Yeats proposed to the 22-year-old Iseult who refused his advances. He had known her since she was four and often referred to her as his darling child. Many Dubliners suspected that Yeats was her father.
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 Gonne made headlines during the Second World War when she was brought to trial for harbouring Hermann Görtz, a German parachutist, a crime to which she confessed but was acquitted.
Iseult was not acknowledged as her mother’s daughter in Maud Gonne’s will when Gonne died in 1953. Iseult died a year later.