Mirren joined the Royal Shakespeare Company, a prestigious and influential theatre company. This marked a significant step in her professional acting career, providing opportunities to work with renowned directors and actors in classic and contemporary plays.

During her time with the RSC, Mirren took on a variety of roles, showcasing her versatility and talent. Some notable performances included roles in productions of 'Troilus and Cressida,' 'The Taming of the Shrew,' and 'Hamlet.' She became known for her strong stage presence and commanding performances.

Mirren starred as Diana in All's Well That Ends Well at the Royal Shakespeare Theatre, also taking on a prominent role in the film Age of Consent