Kay started his fantasy career in 1974 when he was asked by Christopher Tolkien to assist in the editing and preparation of his late father's book, The Silmarillion, for publication. Kay worked on the project in 1974-75, providing editing assistance and helping write a few passages to link areas of Tolkien's material which had no such material. The Silmarillion was published in 1977 to success.
Kay later became a highly acclaimed fantasy writer in his own right, penning a trilogy called The Fionavar Tapestry, a duology called The Sarantine Mosaic and numerous standalones, comprising Tigana, A Song for Arbonne, The Lions of Al-Rassan, The Last Light of the Sun, Ysabel, Under Heaven, River of Stars, Children of Earth and Sky and A Brightness Long Ago. His next novel is scheduled for publication in 2022.