Chanel family matriarch dies aged 99: company
The brand is famed for its creative director Karl Lagerfeld, perfumes such as Chanel No 5 and its distinctive quilted handbags.
Its owners Alain Wertheimer and his brother Gerard are the grandsons of the label's co-founder Pierre Wertheimer.
"Chanel is deeply saddened to confirm the death of Madame Eliane Heilbronn," the group said in a statement, adding that a private funeral will be organised.
In 1947, Eliane Fisher married Jacques Wertheimer, the only son of Pierre Wertheimer, who owned Parfums Chanel and later the Chanel fashion house with his brother Paul.
They had two sons, Alain in 1948 and Gerard in 1951, before divorcing in 1952.
Eliane later married Didier Heilbronn, with whom she had a son, Charles Gregoire.
In her 30s, Eliane Wertheimer studied law at New York University and graduated in 1958.
In 1978, she co-founded Salans Hertzfeld Heilbronn, which became Chanel's private law firm.
Four years earlier, Jacques Wertheimer had handed over the management of Chanel to his son Alain, aged 25.
"Since then, not a dispute, not a project, not an acquisition of a stake has taken place without Eliane Heilbronn's approval", Yann Kerlau said in his book The Dynasties of Luxury.
"Her sons Alain and Gerard, as well as the son from her second marriage Charles Gregoire, owe her everything."
She drafted Karl Lagerfeld's contract in 1982 when he was hired as Chanel's creative director.
Eliane Heilbronn's death comes at a time when Chanel has yet to name a successor to Virginie Viard, who stepped down last June as artistic director of fashion and haute couture.
In May, privately-held Chanel said its sales jumped last year to a record just shy of $20 billion, although profits only edged higher.