Kristel Thornell was born in Parramatta, New South Wales, and outside of Australia has lived in Italy, Mexico, Canada, Finland, the US and France. She holds a B.A. in Italian and French (First Class Hons) for which she won the University Medal from the University of Sydney, an M.A. from the University of New Brunswick, and a Ph.D. from the Writing and Society Research Group at the University of Western Sydney.

Thornell was named one of the Best Young Australian Novelists by The Sydney Morning Herald in 2011. Her first novel, Night Street, co-won the 2009 Australian / Vogel Literary Award and won the 2011 Dobbie Literary Award and the 2010 Barbara Ramsden Award. It also won the 2012 Andrew Eiseman Writers Award for the best book written in Western New York. Night Street was shortlisted for the Glenda Adams Award and the Christina Stead Prize for fiction in the 2011 NSW Premier's Literary Awards, and was included in the Victorian Curriculum Authority's Text Lists. Night Street was published in North America by Goose Lane Editions, and has been optioned for film.

Thornell's second novel, On the Blue Train, was published by Allen & Unwin in 2016, and in Chinese by Lijiang Publishing in 2019. She was awarded an Australia Council for the Arts International Residency in Rome in 2017, and an international residency with the Shanghai Writers' Association in 2021 (scheduled for 2023). Her new novel, The Sirens Sing, will be released on the 7th of September 2022 by HarperCollins/Fourth Estate.