McCormack is best known for her roles in the films Braveheart, Dangerous Beauty, Dancing at Lughnasa and Spy Game. Her other feature film credits include The Land Girls, Shadow of the Vampire, The Weight of Water, A Sound of Thunder and Renaissance. She was nominated for an Olivier Theatre Award in 2001 for Best Supporting Actress for her performance in All My Sons at the National Theatre. Her other stage credits include Vermillion Dreams at the Salisbury Playhouse, Lie of the Mind at the Donmar, Dinner, Free and Honour at the National Theatre and White Horses at the Gate Theatre in Dublin.
In addition to McCormack, the cast of The 39 Steps will include Rupert Degas Stones in his Pockets, Charles Edwards currently appearing on the London stage in Hay Fever and Simon Gregor who previously appeared in The 39 Steps at the West Yorkshire Playhouse. During the course of the play, the four actors will play more than 150 roles.
The 39 Steps is scheduled to officially open on August 14.