Family background and education
Fraser is the first-born of the eight children of Frank Pakenham, 7th Earl of Longford (1905–2001), and his wife, Elizabeth Pakenham, Countess of Longford, née Elizabeth Harman (1906–2002). As the daughter of an earl, she is accorded the courtesy title "Lady" and thus customarily addressed formally as "Lady Antonia".
As a teenager, she and her siblings converted to Catholicism, following the conversions of their parents. Her "maternal grandparents were Unitarians – a non-conformist faith with a strong emphasis on social reform ...". In response to criticism of her writing about Oliver Cromwell, she has said, "I have no Catholic blood". Before his own conversion in his thirties following a nervous breakdown in the Army, as she explains, "My father was Protestant Church of Ireland, and my mother was Unitarian up to the age of 20 when she abandoned it."
She was educated at the Dragon School in Oxford, St Mary's School, Ascot, and Lady Margaret Hall, Oxford; the last was also her mother's alma mater.