Susan Cooper was born in 1935, and grew up in England's Buckinghamshire, an area that was green countryside then but has since become part of Greater London. As a child, she loved to read, as did her younger brother, who also became a writer. Cooper also loved newspapers, and when she was ten she collaborated on a weekly newspaper with the son of her piano teacher; that same year she wrote three plays for a puppet theater and a small book, which she also illustrated. After attending Oxford, where she became the first woman to ever edit that university's newspaper, Cooper worked as a reporter and feature writer for London's Sunday Times; her first boss was James Bond creator Ian Fleming.
Cooper wrote her first book for young readers in response to a publishing house competition; Over Sea, Under Stone would later form the basis for her critically acclaimed five-book fantasy sequence, The Dark Is Rising. The fourth book in the series, The Grey King, won the Newbery Medal in 1976. By that time, Susan Cooper had been living in America for 13 years, having moved to marry her first husband, an American professor, and was stepmother to three children and the mother of two.
Cooper went on to write other well-received novels and several picture books for young readers. She has also written books for adults, as well as plays and screenplays, many in collaboration with the actor Hume Cronyn, whom she married in 1996. They live in Connecticut. When Cooper is not working, she enjoys playing piano and traveling, especially to islands in the Caribbean.