She underwent surgery for lung cancer last year and died at the Malibu home of actor Dick Van Dyke, her partner of 30 years.

Michelle met Lee Marvin while working as an extra in his 1964 movie Ship of Fools. They lived together for six years and she took his last name but never married. The relationship ended in 1970.

At first she accepted payments from him of $833 a month to support her while she tried to resume her career. But after support stopped, she sued for half of everything Marvin had earned during their years together. Her share would have been $1.8m. Her cause was taken up by leading Hollywood’s divorce lawyer Marvin Mitchelson.

The case of Marvin vs Marvin focused a spotlight on the then radical arrangement of cohabiting unmarried couples and the plight of women after relationships ended. At first, the suit was rejected by the courts as having no basis in law. But Mitchelson took her case to the California Supreme Court where in 1976 she won the right to bring suit. He would later say that the day she won the right to walk into court and file suit was the day American marriage and family law changed. Mitchelson coined the term “palimony” and it stuck.

By the time the case of Marvin vs Marvin came to court in 1979, palimony suits were springing up across the country. The case broke new legal ground. But Michelle never received any of Marvin’s fortune. A judge rejected Marvin’s community property request but granted her $104,000 for “rehabilitation”. The award was later overturned on appeal.The case spurred similar trials and established in California law the right of unmarried partners to sue for joint property.

Friends claimed Marvin did not dwell on the case and was not bitter, even though she was forever associated with it. One said: “She just shrugged it off. If Lee Marvin’s name came up, she said he was a great guy.”

Her relationship with Van Dyke began in the late 1970s and they moved to Malibu in 1986. Lee Marvin died in 1987. Besides Van Dyke, Marvin is survived by her sister, a niece and a nephew.