It was previously announced Scottish star Cox, best known for playing media tycoon Logan Roy in Succession, will take on the role of James Tyrone in the autobiographical play, directed by Jeremy Herrin.
Clarkson, who starred opposite Amy Adams in the adaptation of the novel Sharp Objects and is also known for roles in Easy A, The Green Mile and Far From Heaven, will play matriarch Mary Tyrone, while Lawther will appear as Edmund.
Telling a story of love, hate, betrayal, addiction and the fragility of family bonds, it depicts a summer day in the life of the Tyrone family.
McCormack said: “It has been a dream of mine to bring this play to life, since I first read it as a student more than 10 years ago. To be accompanied by such talented actors and have a brilliant director in Jeremy, it is a true gift. I eagerly await the work that is ahead of us in reviving this magnificently tragic and haunting play.”
Director Herrin added: “A great play is always relevant and Long Day’s Journey Into Night is, it’s often argued, the greatest play of the 20th century.
“With its searing honesty and blistering depth of emotion, it must be up there.
“What is impossible to argue with is that we have the best cast and, in Lizzie Clachan, one of the most exciting designers in the country, to discover what makes O’Neill’s masterwork relevant for now.
“I can’t wait to bring this classic to life. I anticipate a feast of fine acting and vivid performances in what I hope to be a high definition production.”
Long Day’s Journey Into Night will begin previews at Wyndham’s Theatre from March 19 2024 with opening night on April 2 2024.