As a result of her work for the National Youth Theatre, Mirren was invited to join the Royal Shakespeare Company (RSC). While with the RSC, she played Castiza in Trevor Nunn's 1966 staging of The Revenger's Tragedy, Diana in All's Well That Ends Well (1967), Cressida in Troilus and Cressida (1968), Rosalind in As You Like It (1968), Julia in The Two Gentlemen of Verona (1970), Tatiana in Gorky's Enemies at the Aldwych (1971), and the title role in Miss Julie at The Other Place (1971). She also appeared in four productions, directed by Braham Murray for Century Theatre at the University Theatre in Manchester, between 1965 and 1967.
In 1970, the director and producer John Goldschmidt made a documentary film, Doing Her Own Thing, about Mirren during her time with the Royal Shakespeare Company. Made for ATV, it was shown on the ITV network in the UK. In 1972 and 1973, Mirren worked with Peter Brook's International Centre for Theatre Research and joined the group's tour in North Africa and the US, during which they created The Conference of the Birds. She then rejoined the RSC, playing Lady Macbeth at Stratford in 1974 and at the Aldwych Theatre in 1975. In 1976, she appeared with Laurence Olivier, Alan Bates and Malcolm McDowell in a production of Harold Pinter's The Collection as part of the Laurence Olivier Presents series.
Sally Beauman reported, in her 1982 history of the RSC, that Mirren—while appearing in Nunn's Macbeth (1974), and in a letter to The Guardian newspaper—had sharply criticised both the National Theatre and the RSC for their lavish production expenditure, declaring it "unnecessary and destructive to the art of the Theatre", and adding, "The realms of truth, emotion and imagination reached for in acting a great play have become more and more remote, often totally unreachable across an abyss of costume and technicalities..." This started a big debate, and led to a question in parliament. There were no discernible repercussions for this rebuke of the RSC.
At the West End's Royal Court Theatre in September 1975, she played the role of a rock star named Maggie in Teeth 'n' Smiles, a musical play by David Hare; she reprised the role the following year in a revival of the play at Wyndham's Theatre in May 1976. Beginning in November 1975, Mirren played in West End repertory with the Lyric Theatre Company as Nina in The Seagull and Ella in Ben Travers's new farce The Bed Before Yesterday ("Mirren is stirringly voluptuous as the Harlowesque good-time girl": Michael Billington, The Guardian). At the RSC in Stratford in 1977, and at the Aldwych the following year, she played a steely Queen Margaret in Terry Hands' production of the three parts of Henry VI, while 1979 saw her 'bursting with grace', and winning acclaim for her performance as Isabella in Peter Gill's production of Measure for Measure at Riverside Studios. Mirren has appeared in a large number of films throughout her career. Some of her earlier film appearances include roles in Herostratus (1967, Dir. Don Levy), A Midsummer Night's Dream (1968), Age of Consent (1969), and O Lucky Man! (1973).
