Joan Evans was the only child of Evans's third marriage, to Maria Millington Lathbury. She was born at Nash Mills on 22 June 1893 when her father was 70 and her mother 37. She lived at Nash Mills until 1906 when the family moved to the newly built Britwell at Berkhamsted. Her mother and father travelled extensively, sharing a mutual interest in antiquity and Joan seems mainly to have been brought up by her beloved nanny, Caroline Hancock, who came to look after Joan when she was eleven months old and stayed for 67 years. From the age of two Joan spent happy summer holidays with nanny Hancock and her parents and sister at their home in Milton Keynes, Buckinghamshire. She dedicated her memoir Prelude and Fugue to Nanny Hancock who died in 1961, aged 97.

Joan attended the local Grammar School in Berkhamsted. After visiting Rome with her mother when she was 21, Joan changed her mind about reading for the Diploma in Anthropology as she had intended, and instead read classical archaeology at St. Hugh's, Oxford. She successfully gained her diploma, with honours, in 1916 (women were not granted degrees at this time); a certificate of letters in 1919 and a BLitt. in 1920. She was the only female archaeology student and one of the few fellow archaeology students at the time was an Australian named Gordon Childe. (Childe was at Queens College and one of his supervisors was Joan's brother Arthur; he went on to a distinguished career as professor of archaeology at Edinburgh.) She then worked as St. Hugh's librarian until 1922. Having grown up surrounded by her father's extensive and varied collections, and being allowed to look at these collections and even help him write the labels on occasion, gave her the enthusiasm and interest to follow him in collecting. She collected beads whilst still a very young child, some from crackers, others given to her by her father from his travels, and bits of amber collected by him from the Suffolk coast. She mentions (in Prelude and Fugue) a visitor giving her a Pistrucci crown to add to her own coin collection, when she was about nine years old. In her second year at St. Hugh's she 'acquired a pair of old French candlesticks, once in the Brissac family, through a college friend who turned out to be an unknown third cousin' and ' I have bought a gilt wood torchere, about 4 ft. high, about 1879, I guess, and a good one' (Prelude and Fugue). She collected gems and jewels, eventually giving her large collection to the Victoria and Albert Museum, where it remains today.

From the age of four, Joan began travelling abroad with nanny Hancock at the invitation of her parents; when she was eight her father took her to see the gravel pits of Saint-Acheul; he also took her to Germany to see the places where he had travelled as a young man with his brother Arthur. They often made purchases in the antique shops in the towns they visited.

Joan Evans was the first woman to be elected as President of the Society of Antiquaries, a position her father and brother had held before her; she received the gold medal of the Society in 1973. At various times she was president of the Royal Archaeological Institute; fellow of the Royal Historical Society and the Royal Society of Literature; DLitt, London and Oxford, honorary LLD, Edinburgh, honorary LittD, Cambridge and honorary FRIBA. She was appointed a Dame of the British Empire in 1976.

Joan Evans was extremely generous, giving her time and money to various causes. She was a major benefactor of St. Hugh's College, and was instrumental in assisting in the purchase of the ridge above her home at Wotton under Edge for the National Trust.

England & Wales, Civil Registration Death Index, 1916-2007