Bruno Jacquelin, of the Brigitte Bardot Foundation for the protection of animals, told The Associated Press she died at her home in southern France on Sunday, and would not provide a cause of death.
He said no arrangements have yet been made for funeral or memorial services. She had been hospitalised in November.
French President Emmanuel Macron led tributes to the film legend.
"Her films, her voice, her dazzling fame, her initials, her sorrows, her generous passion for animals, her face that became Marianne - Brigitte Bardot embodied a life of freedom," he said.
"A French existence, a universal radiance. She moved us. We mourn a legend of the century."
Bardot became an international celebrity as a sexualised teen bride in the 1956 movie And God Created Woman.
Directed by her then-husband, Roger Vadim, it triggered a scandal with scenes of the long-legged beauty dancing on tables naked.
At the height of a cinema career that spanned some 28 films and three marriages, Bardot came to symbolise a nation bursting out of bourgeois respectability.
Her tousled, blonded hair, voluptuous figure and pouty irreverence made her one of France's best-known stars.
Such was her widespread appeal that in 1969 her features were chosen to be the model for Marianne, the national emblem of France and the official Gallic seal.
Bardot's face appeared on statues, postage stamps and even on coins.
Her second career as an animal rights activist was equally sensational.
She travelled to the Arctic to blow the whistle on the slaughter of baby seals; she condemned the use of animals in laboratory experiments; and she opposed sending monkeys into space.
"Man is an insatiable predator," Bardot told The Associated Press on her 73rd birthday, in 2007.
"I don't care about my past glory. That means nothing in the face of an animal that suffers, since it has no power, no words to defend itself."
Her activism earned her compatriots' respect and, in 1985, she was awarded the Legion of Honour, the nation's highest decoration.
Later, however, she fell from public grace as her animal protection diatribes took on a decidedly extremist tone and her far-right political views sounded racist as she frequently decried the influx of immigrants into France, especially Muslims.
Bardot was convicted five times in French courts of inciting racial hatred.
Bardot's 1992 marriage to fourth husband Bernard d'Ormale, a one-time adviser to former National Front leader Jean-Marie Le Pen, contributed to her political shift. She described the outspoken nationalist as a "lovely, intelligent man".
In 2012, she caused controversy again when she wrote a letter in support of Marine Le Pen, the current leader of the party — now renamed National Rally — in her failed bid for the French presidency.
In 2018, at the height of the #MeToo movement, Bardot said in an interview that most actors protesting sexual harassment in the film industry were "hypocritical" and "ridiculous" because many played "the teases" with producers to land parts.
She said she had never had been a victim of sexual harassment and found it "charming to be told that I was beautiful or that I had a nice little ass".
Among her films were A Parisian (1957); In Case of Misfortune, in which she starred in 1958 with screen legend Jean Gabin; The Truth (1960); Private Life (1962); A Ravishing Idiot (1964); Shalako (1968); Women (1969); The Bear And The Doll (1970); Rum Boulevard (1971); and Don Juan (1973).
With Reuters
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