She was born at Birkenhead near Liverpool, into a working-class family, and it is a well-known piece of trivia that she once worked in a Boots pharmacy store. Having studied acting at RADA, Jackson made her professional stage debut in Terence Rattigan's Separate Tables in 1957 and her film debut in This Sporting Life in 1963.

Fame came with Jackson's starring role in the controversial Women in Love (1969) gaining her first Oscar, and another controversial role as Tchaikovsky's nymphomaniac wife in Ken Russell's The Music Lovers added to her image of being prepared to do almost anything for her art. She confirmed this by having her head shaved in order to play Queen Elizabeth I of England in the BBC's 1971 blockbuster serial, Elizabeth R. In this year, she also appeared in a BBC Morecambe and Wise Show, playing Cleopatra in a comedy sketch which is generally recognised as one the funniest sequences in British TV history. Film maker Melvin Frank watched this and saw her comedic potential and offered her the lead female role in his next project. She earned a second Oscar for this particular comic role in A Touch of Class (1973), and Eric and Ernie apparently sent her a telegram saying: 'Stick with us kid, and we'll get you a third!'. She also portrayed Queen Elizabeth on a film about the life of Mary, Queen of Scots and she has been recognised as one of Britain's leading actresses. In 1978, she was made a Commander of the Order of the British Empire.

She retired from acting in order to enter the House of Commons in the United Kingdom general election, 1992 as the Labour MP for the Hampstead & Highgate. After the United Kingdom general election, 1997, she was appointed a junior minister in the government of British Prime Minister, Tony Blair, with responsibility for London Transport, a post she resigned before an attempt to be nominated as the Labour Party candidate for the election of the first Mayor of London in 2000. The nomination was eventually won by Frank Dobson, who lost the election to Ken Livingstone, the independent candidate. In the United Kingdom general election, 2005, she received 14,615 votes, representing 38.29f the votes cast in the constituency.

As a high profile backbencher she has become a regular critic of Blair over his plans to introduce top-up fees. She also called for him to resign following the Judicial Enquiry by Lord Hutton in 2003 surrounding the reasons for going to war in Iraq and the death of government adviser Dr. David Kelly. Jackson is generally considered to be a traditional left-winger, often disagreeing with the dominant Blairite governing centre-right faction in the Labour Party. By October 2005, her problems with Blair's leadership swelled to a point where she threatened to challenge the Prime Minister as a stalking horse candidate in a leadership contest if he does not stand down within a reasonable amount of time. Glenda Jackson is also seen as a possible dark horse contender to succeed Tony Blair when he leaves office.

She has one son by her ex-husband, Roy Hodges.