Smith was born, the daughter of Margaret (née Hutton), a Glasgow-born secretary, and Nathaniel Smith, a Newcastle upon Tyne-born public health pathologist who worked at Oxford University. She has older twin brothers, Alistair and Ian. Smith studied at Oxford High School, although she has been quoted as not having enjoyed her school experience.

Smith has had an extensive career both on screen and in live theatre, and is known as one of Britain's pre-eminent actresses. She began her career at the Oxford Playhouse with Frank Shelley and made her first film in 1956.

She became a fixture at the Royal National Theatre in the 1960s, most notably for playing Desdemona in Othello opposite Laurence Olivier and winning her first Oscar nomination for her performance in the 1965 film version.

In 1969 she won the Academy Award for Best Actress for her performance as an unorthodox Scottish schoolteacher in The Prime of Miss Jean Brodie, a role originally created on stage by Vanessa Redgrave in 1966. She was also awarded the 1978 Academy Award for Best Supporting Actress for her role as the brittle actress Diana Barrie in California Suite, acting opposite Michael Caine.

Afterwards, on hearing that Michael Palin was about to embark on a film (The Missionary) with Smith, Caine is supposed to have humorously telephoned Palin, warning him that she would steal the film. She also starred with Palin in the dark but hilarious film A Private Function in 1984.

Smith appeared in Sister Act in 1992 and had a major role in the 1999 film Tea With Mussolini, where she appeared as the formidable Lady Hester. Indeed, many of her more mature roles have centred on what Smith refers to as her "gallery of grotesques", playing waspish, sarcastic or plain rude characters.

Recent examples of this would include the judgemental sister in Ladies in Lavender and the cantankerous snob Constance Trentham in Gosford Park, for which she received another Oscar nomination.

Other notable roles include the querulous Charlotte Bartlett in the Merchant-Ivory production of A Room with a View, a vivid supporting turn as the aged Duchess of York in Ian McKellen's film of Richard III, and a little known but powerful performance as Lila Fisher in the 1973 film Love and Pain and the Whole Damn Thing opposite Timothy Bottoms. Due to the international success of the Harry Potter movies, she is now widely known for playing the role of Professor Minerva McGonagall.

She appeared in numerous productions at the Stratford Shakespeare Festival in Stratford, Ontario, to extraordinary acclaim from 1976 through 1980.

On stage, her many roles include the title character in the stage production of Alan Bennett's The Lady in the Van and starring as Amanda in a revival of Noel Coward's Private Lives. She won a Tony Award in 1990 for Best Actress in a Play for Lettice and Lova

ge, in which she starred as an eccentric tour guide in an English stately home. She was awarded Commander of the Order of the British Empire (CBE) in 1970, and was raised to Dame Commander (DBE) in 1990.