She is best known for The Dark Is Rising, a contemporary fantasy series set in England and Wales, which incorporates British mythology such as the Arthurian legends and Welsh folk heroes.

She attended Slough High School and then earned a degree in English at Somerville College at the University of Oxford, where she was the first woman to edit the undergraduate newspaper Cherwell.

During that period she began work on the series The Dark Is Rising and finished her debut novel, the science fiction Mandrake, published by Hodder & Stoughton in 1964.

[9] The history of the Marshfield area was the basis for her 2013 book Ghost Hawk, in which the spirit of a Wampanoag, whose people were decimated by European disease, witnesses the transformation of Massachusetts by the Plymouth Colony.

[13][14] In April 2017, Cooper gave the fifth annual Tolkien Lecture at Pembroke College, Oxford, speaking on the role of fantasy literature in contemporary society.

[16][17] The American Library Association's Margaret A. Edwards Award recognises one writer and a particular body of work for "significant and lasting contribution to young adult literature".

The citation observed, "In one of the most influential epic high fantasies in literature, Cooper evokes Celtic and Arthurian mythology and masterly world-building in a high-stakes battle between good and evil, embodied in the coming of age journey of Will Stanton.