Faithfull was born in South Africa, the daughter of a nurse and an army officer. When her father was killed in the First World War in 1916, her mother returned to England. She was educated at Bournemouth and studied then at the Sorbonne, which she financed by work in a nursery in Paris. In 1978 the University of Warwick made her an Honorary Doctor of Letters and in 1995, she also received the same degree from the Oxford Brookes University. She was elected an honorary fellow of St Hilda's College, Oxford in 1992.