Susan Mary Cooper was born on May 23, 1935, in Burnham, Buckinghamshire, England. She attended Somerville College of Oxford University, receiving her master's degree in 1956.

Upon graduation she was hired as a reporter and feature writer for the London Sunday Times, where she worked from 1956 to 1963. In 1963 she married Nicholas J. Grant, a college professor, with whom she had two children. She and her husband moved to the United States later that year, and from 1963 to 1972 Cooper was a columnist for the Western Mail, Cardiff, Wales.

In 1965 Cooper published in England a book based upon her dispatches, Behind the Golden Curtain: A View of the U.S.A., which appeared in America a year later. Her first fantasy novel, Over Sea, Under Stone, came out in 1965. She did not originally envision this book as part of a series, and eight years passed before she published a...