Leith was born in Belfast, Northern Ireland, when her family was living in the linen town of Lisburn.
After elementary and secondary schooling in London and Basel, Switzerland, she moved to Montreal with her family as an adolescent.
She is the author, most recently, of The Girl from Dream City: A Literary Life, published by the University of Regina Press in April 2021.
Earlier works of nonfiction works include the literary history Writing in the Time of Nationalism, which The Globe and Mail called "a very fine book," "written in clear, exhilarating prose,"[4] and Marrying Hungary, as well as Introducing Hugh MacLennan's Two Solitudes.
She is the author of three novels: Birds of Passage (1993), The Tragedy Queen (1995), and The Desert Lake (2007) all published by Signature Editions.