She fought cancer while filming the eighth Harry Potter movies and Nanny McPhee and The Big Bang because she didn't want to disappoint fans
Winner of 2 Oscars, 3 Golden Globes, 5 BAFTAs, 4 Emmys and 2 SAGs among other awards.
Thank you for giving life to Minerva McGonagall and
A legend of British stage and screen, she won two Oscars during her career - for The Prime of Miss Jean Brodie in 1970 and California Suite in 1979.
She had four other nominations, and received seven Bafta awards.
Leading the tributes, Prime Minister Keir Starmer said Dame Maggie "was beloved by so many for her great talent, becoming a true national treasure whose work will be cherished for generations to come".
In the Harry Potter films, Dame Maggie played the acerbic Professor Minerva McGonagall, famous for her pointed witch's hat and stern manner with the young wizards at Hogwarts.
In hit ITV drama Downton Abbey, she played Violet Crawley, the Dowager Countess of Grantham, the grand matriarch who excelled at withering one-liners through the show's six series.
A statement from her sons Toby Stephens and Chris Larkin said: "It is with great sadness we have to announce the death of Dame Maggie Smith.
"She passed away peacefully in hospital early this morning, Friday 27th September.
"An intensely private person, she was with friends and family at the end. She leaves two sons and five loving grandchildren who are devastated by the loss of their extraordinary mother and grandmother."
They thanked "the wonderful staff at the Chelsea and Westminster Hospital for their care and unstinting kindness during her final days".
They added: "We thank you for all your kind messages and support and ask that you respect our privacy at this time."
Tributes were also paid by her co-stars.
Hugh Bonneville, who appeared in Downton Abbey, said: “Anyone who ever shared a scene with Maggie will attest to her sharp eye, sharp wit and formidable talent.
"She was a true legend of her generation and thankfully will live on in so many magnificent screen performances. My condolences to her boys and wider family."
Dame Maggie also reprised her role for the two Downton Abbey films.
In 2022's Downton Abbey: A New Era, her character died of the illness she revealed at the end of the 2019 film, to the huge upset of her family and friends.
Lesley Nicol, who played Downton Abbey’s cook Mrs Patmore, told BBC Radio Ulster: "It's a very close group of people so we're all devastated to think she's not around any more."
Downton followed the success of 2002 period drama Gosford Park, which earned Dame Maggie both Oscar and Bafta nominations for playing Dowager Countess of Trentham.
Dame Kristin Scott-Thomas, who starred alongside Dame Maggie in Gosford Park plus 2005's Keeping Mum and 2014's My Old Lady, said she "took acting very seriously but saw through the nonsense and razzmatazz".
"She really didn’t want to deal with that," Dame Kristin added.
"She had a sense of humour and wit that could reduce me to a blithering puddle of giggles. And she did not have patience with fools. So you had to be a bit careful. I absolutely adored her.
"The last time I saw her, she was very cross about being old. 'Maddening' I think she said. Much loved, much admired and irreplaceable."
In his statement, the prime minister said Dame Maggie "introduced us to new worlds with the countless stories she acted over her long career".
"Our thoughts are with her family and loved ones. May she rest in peace," he wrote.
A National Theatre spokesperson said her career "spanned the theatrical, film and television world without equal".
Praising her stage performances, the statement added: "She will forever be remembered as one of the greatest actors this country has had the inestimable pleasure of witnessing."
Bafta added that she was a "legend of British stage and screen", praising her five competitive Bafta wins, plus the special award and fellowship she received from the organisation.