As a child she attended Raine's Foundation School and went on to train at the pioneering East 15 Acting School, an establishment inspired by the works of Joan Littlewood, receiving the first-ever scholarship to the school. She has since worked in theatre, television, film, and radio, starting with "Diary of a Young Man", a series written for her by John McGrath and Troy Kennedy Martin, directed by Ken Loach.
Mitchell is on the Board of Directors of The Unity Theatre Trust, a Trustee of Arbours (a psychotherapeutic care centre) and is a Patron of Clean Break, a theatre and training company for female ex-offenders.
In 2003 Mitchell was a nominee for Best Actress in the Evening Standard Awards and the Laurence Olivier Awards for her performance as Martha in Through The Leaves, first at The Southwark Playhouse and later the Duchess Theatre, London. In 1992 she received the accolade of "Performance of The Year" by The Independent on Sunday for her Hecuba at The Gate Theatre. In 1984 she received the Pye Award for Female who had the greatest impact on television for her role as Dolly Rawlins in the groundbreaking crime series Widows, written by Lynda La Plante.
Her work as a director and writer includes: Voices From Prison (RSC Platform), Cathy Come Home (first stage adaptation, Pit Theatre), Ever After (co-written with Kathy Itzen), Kiss and Kill (co-written with Susan Todd for Monstrous Regiment and nominated for the Susan Smith Blackburn Prize). She directed the world premiere of Barry Keeffe’s Sus, at the Royal Court Theatre).
For the Royal Shakespeare Company her roles include Hecuba, Aethra, and the nurse in Tantalus at the Barbican (RSC), Frieda Lawrence in Divine Gossip, and The Woman in Edward Bond’s War Plays I, II, III. Tantalus was a coproduction of the RSC and the Denver Center for the Performing Arts in the U.S. where it received its world premiere in a mammoth performance of the three parts given over 10 hours.
Working for the leading companies in the UK she was: Helen in The Road to Mecca (Royal Exchange Theatre, Manchester), Mrs. Malaprop in The Rivals (Nottingham Playhouse), Marge in A Colder Climate (Royal Court), A Matter of Life and Death (Royal National Theatre), Brenda in Mary Barnes (Royal Court), Guinevere in Guinevere (written for her by Pam Gems, Soho Poly), Mrs. Prentice in What the Butler Saw (the Crucible Theatre, Sheffield). Most recently she co-starred in Whose Life Is It Anyway? in London’s West End with Kim Cattrall and Janet Suzman.
For television, Mitchell has starred in many of the most popular UK television series ranging from drama to comedy, including Z-Cars, Talking to a Stranger, Up the Junction, Play for Today, Upstairs, Downstairs, Within These Walls, Bergerac, Taggart, The Detectives, Kavanagh QC, Maigret, The Bill, EastEnders, French & Saunders, and Gimme Gimme Gimme (written for her by Jonathan Harvey). She co-stars as Lillian in the forthcoming Granada production of Jane Hall’s Big Bad Bus Ride, and was most recently seen as Rita in Tunnel of Love for Thames. As Dolly Rawlins in Widows I, II and She’s Out (written for her by Lynda La Plante) she won acclaim and affection.
Films include: Mrs. Bolton, Lady Chatterley’s Lover, Murder by Decree, Full Circle, Yanks, Paper Marriage, What's Your Number 41?