Mary Morley Crapo was born to a wealthy French-American family in Detroit, Michigan. She attended the Hartridge School, then Vassar College, and did graduate work at Columbia University. Her Ph.D. dissertation was developed into a book published as Playwriting for Elizabethans, 1600-1605 (1949). In 1939, she married Donald Frizell Hyde, a lawyer and avid book collector in New York. Mrs. Hyde and her husband bought Dr. Samuel Johnson's silver teapot in 1941, and went on to buy more than 500 of his surviving letters, including some written to his friend Hester Thrale, as well as some of Johnson's diaries and Mrs. Thrale's private journals. They turned their estate of Four Oaks Farm near Somerville, New Jersey, into a replica of Streatham Park, the original home of Mrs. Thrale, built a fireproof library, and filled the house with their collections. They also founded and hosted dinners for the Johnsonians, a select group of Johnson scholars and collectors. Mrs. Hyde used the books, manuscripts, letters from the library to complete several works on members of the Johnson circle, including The Impossible Friendship: Boswell and Mrs. Thrale (1972) and The Thrales of Streatham Park (1975). After World War II, Mrs. Hyde scored a major addition to the collection with the acquisition of James Boswell's papers found at Malahide Castle in Ireland, which she obtained through Col. Ralph Isham. The collaboration with the eccentric Col. Isham inspired her to write a one-act play, Levee at Fifty-Third Street. She also edited Bernard Shaw and Alfred Douglas, A Correspondence. Many of her short works were collected as Mary Hyde Eccles: A Miscellany of her Essays and Addresses (2002). After the death of her first husband, Mary remarried in 1984 to the British politician Sir David McAdam Eccles, 1st Viscount Eccles, making her Viscountess Eccles. With her second husband, she founded the David and Mary Eccles Centre for American Studies at the British Library in 1992. She was made an honorary fellow of Pembroke College at Oxford University and a Benjamin Franklin Fellow of the Royal Society of Arts.