Mary Cartwright was born on 17 December 1900, in Aynho, Northamptonshire, where her father William Digby was vicar. Through her grandmother Jane Holbech, she descended from poet John Donne and William Mompesson, Vicar of Eyam. She had four siblings, two older and two younger: John (born 1896), Nigel (born 1898), Jane (born 1905), and William (born 1907). Her early education was at Leamington High School (1912–1915) then Gravely Manor School in Boscombe (1915–1916) before completion in Godolphin School in Salisbury (1916–1919).