Born as Margaret Helen Anderson, Margaret Greville was the daughter of William McEwan (1827-1913), a brewery multimillionaire, who later was elected as an M.P. (Member of Parliament). Her mother was Helen Anderson (1835/1836–1906), but she was not married to William when Margaret, their daughter was born. In fact, it was not until 1885, when Margaret was 21, and the family had moved to London, that William McEwan and Helen Anderson married. In 1891, when she was 28, Margaret Anderson married Hon. Ronald Henry Fulke Greville, eldest son of the 2nd Baron Greville. They had no children; he died in 1908. She was a close friend of Queen Mary. She bequeathed all her jewels to Queen Elizabeth The Queen Mother, including a diamond necklace reputedly belonging to Marie Antoinette, a pair of diamond chandelier earrings and a tiara and ruby necklace by Boucheron, all of which are in possession of the British Royal Family. She also left £20,000 to Princess Margaret, as well as £25,000 to Queen Victoria Eugenia of Spain. Margaret Greville was named a Dame Commander of the Order of the British Empire (DBE) in 1922. At her death, her estate Polesden Lacey in Great Bookham, Surrey, was bequeathed to the National Trust. She is buried on the grounds of Polesden Lacey.