She was born in Bradford, Yorkshire, in 1974. She lives in the United Kingdom. She has a message board at Night Shade Books, and sample chapters of her novels are free online on the books page of her website.

Ms. Swainston has previously worked in a variety of jobs, including as a qualified archaeologist (with a degree from Girton College, University of Cambridge, and a research degree from the University of Wales), being employed on a dig that researched the oldest recorded burial site in the UK, Paviland Cave, as well as in Hayonim Cave in Israel. Additional occupations include working for an ethical company developing pharmaceuticals from cannabis, as an assistant in a zoo vet's lab and as a researcher for the MoD.

Swainston lists William Burroughs, Angela Carter and M. John Harrison as her major influences and Mervyn Peake as her favourite author. She likes the weird eccentric wordplay and nonsense poetry of Lewis Carroll, Edward Lear, a tradition continued by Douglas Adams and Jeff Noon's Vurt. She is widely read, especially in the ouvres of Dumas, Dickens, Vonnegut, Huxley, T.S. Eliot, Louis de Bernieres, Orhan Pamuk, Alexander Trocchi, the fantasy of Gene Wolfe, and adventure stories such as Robert Louis Stevenson.

Swainston's work so far has been set in 'the Fourlands' Castle series, which the author has described as a secret childhood paracosm, further influenced by aspects of her later adult life, including the competitive academic world. The novels centre on the life of 'the Circle', an elite group of immortals created and sustained by the Emperor, a near god-like figure engaged in a prolonged conflict with insectoid creatures, apparently from another world. Told in the first person, the novels follow the life of Jant, a winged humanoid with a distinctly flawed personality. The Castle series is also marked by the existence of multiple worlds, including the fantastic, baroque 'Shift'.

Whilst characterised by others as a member of the fantasy literary genre the New Weird, which aims to reform fantasy literature by transcending its traditional boundaries, Swainston has argued against labelling writers, including herself, within genres, arguing that good fantasy and mainstream literature instead form a continuum. Nonetheless she has been critical of the conservative nature of much commercial fantasy writing, and her approach embraces narrative themes unfamiliar to conventional fantasy, including drug use and sexual scenes, alongside the hyper-realistic depiction of warfare. Whereas much of the New Weird genre embraces the idea of a deliberate subversion of the established fantasy tropes with a specific readership in mind, however, Swainston has preferred to describe her work as appealing to the ongoing deep structures of universal storytelling, as literature written as much in response to the author's own needs than as a response to specific market requirements.

The Castle books

• The Year of Our War (Gollancz SF, 2004) ISBN 978-0575076426
• The Year of Our War (Gollancz SF, 2006) ISBN 978-0575077980
• No Present Like Time (Gollancz SF, 2005, hardcover) ISBN 978-0575070066
• No Present Like Time (Gollancz SF, 2006, paperback) ISBN 978-0575077980
• The Modern World (Gollancz SF, 2007, paperback) ISBN 978-0575082212
• The Castle Omnibus: "The Year of Our War", "No Present Like Time", "The Modern World" (Gollancz SF, 2009, paperback) ISBN 978-0575091252
• Above the Snowline (Gollancz SF, 2010, hardcover) ISBN 978-0575081581