Reid was born in Whitstable, Kent, England. Her father was a doctor in the British Army. She lived in Germany, Africa, and the United States before settling in Canada with her family in 1964.

She studied acting at McGill University, receiving a Bachelor of Arts degree in 1972, and at the Banff Centre for the Arts.

Reid met McCowan Thomas doing summer stock theatre and married him in 1977. They have two children, Alec and Julia.

She has twice won the Dora Mavor Moore Award, in 1993 for Fallen Angels and in 1995 for Six Degrees of Separation. She won an Elizabeth Sterling Haynes Award (Sterling Award) for her performance in August: Osage County.

In 2006, she was made a Member of the Order of Canada She received The Barbara Hamilton Award in 2008. and an award of excellence from ACTRA Toronto in 2010.

Fiona Reid is one of Canada’s best known stage actors, having performed in theatres across the country, including five seasons with the Stratford Festival and twelve seasons at the Shaw Festival, as well as theatres in Great Britain and the U.S.. Over her career her performances have garnered her two Dora Mavor Moore awards, a Jessie Award (Vancouver) and a Sterling Award (Edmonton). In 2015, Fiona received the Toronto Critics’ Award for her performance of Sonia in Vanya, Sonia, Masha and Spike (Mirvish Productions).

In 2016, Reid starred as Queen Elizabeth II in the Mirvish Productions presentation of The Audience at the Royal Alexandra Theatre in Toronto.

In 2019 Fiona began her run in Harry Potter and the Cursed Child on Broadway.