Michelle Triola Marvin, whose landmark lawsuit against her former lover, Dirty Dozen actor Lee Marvin, placed the word "palimony" into family law and changed the legal rights of unmarried partners, has died at 76.

She had surgery for lung cancer last year and died at the Malibu home of actor Dick Van Dyke, her partner of 30 years, said family spokesman Bob Palmer.

Michelle Marvin's birth name was Triola and she met Lee Marvin while working as an extra on his 1964 film 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 £504 a month to support her while she tried to resume her singing and acting career. But after support cheques stopped she sued for half of everything Marvin had earned during their years together; her share would have been just over €1 million.

Her cause was taken up by one of Hollywood's most colourful divorce lawyers, Marvin Mitchelson, who launched what was a campaign to change the law.

The case of Marvin versus Marvin focused a spotlight on the then radical arrangement of cohabiting unmarried couples and the plight of women after such relationships ended.

At first, the case was rejected by the courts as having no basis in law. But Mitchelson took it to the California Supreme Court where in 1976 his client won the right to bring suit.

Mitchelson, known for his pursuit of multi-million-dollar divorce cases, sought to win the same rights for Marvin as she would have under alimony laws if the couple had married. He coined the term 'palimony' and it stuck.

By the time the case of Marvin versus Marvin came to court in 1979, palimony suits were springing up across America. At a time when live-in relationships without marriage had no place in the law, the case broke new legal ground. But Michelle Marvin never received any of Lee Marvin's fortune. A judge rejected her community property request but granted her $104,000 for "rehabilitation". The award was later overturned on appeal.

Although Marvin came away with no money, the sensational case spurred similar trials and established in California law the right of unmarried partners to sue for joint property on grounds that their partners had broken a relationship contract.

Marvin had argued that she gave up her career to become the actor's "cook, companion and confidante" and he had promised to support her for life. He denied that contention.