(September 25, 1956 - 1977) (divorced) (6 children)
From 1956 until their divorce in 1977, she was married to Sir Hugh Fraser (1918–1984), a descendant of Scottish aristocracy 14 years her senior and a Roman Catholic Conservative Unionist MP in the House of Commons (sitting for Stafford), who was a friend of the American Kennedy family. They had six children: three sons, Benjamin, Damian, and Orlando; and three daughters, Rebecca Fitzgerald, wife of barrister Edward Fitzgerald, QC, Flora Fraser and Natasha Fraser-Cavassoni. All three daughters are writers and biographers. Benjamin Fraser works for JPMorgan, Damian Fraser is the managing director of the investment banking firm UBS AG (formerly S.G. Warburg) in Mexico, and Orlando Fraser is a barrister specializing in commercial law (Wroe). Antonia Fraser has 18 grandchildren.
On 22 October 1975, Hugh and Antonia Fraser, together with Caroline Kennedy, who was visiting them at their Holland Park home, in Kensington, west London, were almost blown up by an IRA car bomb placed under the wheels of his Jaguar, which had been triggered to go off at 9 am when he left the house; the bomb exploded killing a noted cancer researcher, Gordon Hamilton Fairley. Fairley, a neighbour of the Frasers, had been walking his dog, when he noticed something amiss and stopped to examine the bomb.