Miss Radmacher, 39, is one of Germany's richest women
A court ruling over a divorced couple's pre-nuptial agreement could pave the way for such contracts to become legally binding in England and Wales.
Katrin Radmacher, a German heiress, has overturned an earlier court decision to award her ex-husband £5.8m of her £100m fortune despite their agreement.
Frenchman Nicolas Granatino had agreed not to make a claim if they divorced.
Such contracts are enforceable in Germany, where the couple's was signed, but not in England where they married.
They are also enforceable in Mr Granatino's home country.
Miss Radmacher, one of Germany's richest women, won a ruling from the Court of Appeal that such contracts should be taken into account by the courts when they divide assets after a marriage fails.
Appeal judge Lord Justice Thorpe said he believed it had become "increasingly unrealistic" for courts to disregard pre-nuptial agreements.
"It reflects the laws and morals of earlier generations," he said.
"It does not sufficiently recognise the rights of autonomous adults to govern their future financial relationship by agreement in an age when marriage is not generally regarded as a sacrament and divorce is a statistical commonplace."
He said a "carefully fashioned contract" should be available as an alternative to the "stress, anxieties and expense" of going through the court.
Mr Granatino is expected to seek permission to take the case to the House of Lords.
Miss Radmacher, 39, said she was "delighted" by the decision.
"Ultimately, this case has been about what I regard as a broken promise," she said.
"The agreement was at my father's insistence as he wanted to protect my inheritance - this is perfectly normal in our countries of origin, France and Germany. Like all wealthy parents, he feared gold-diggers.
"As an heir himself, Nicolas perfectly understood this. The agreement gave me reassurance that Nicolas was marrying me because he loved me as I loved him... that we were marrying for the right reasons."
Her solicitor, Ayesha Vardag, said: "In a landmark judgment, three of the most highly respected judges in the land have ruled that pre-nups can be decisive in determining the financial division on divorce.
"The Court of Appeal, in a carefully reasoned, thoroughly modern judgment has enabled English matrimonial law to catch up with the rest of the world.
"From today grown-ups can agree in the best of times what will happen in the worst of times."
Legal analyst Joshua Rozenberg said it was the first time a senior court had given "a great deal of weight" to a pre-nuptial agreement.
He said it would not happen in every case and the issue would remain unclear until Parliament changed the law.
The couple's pre-nuptial was signed in Germany before the couple married in London in 1998.
The pair's marriage was said to have broken down after Mr Granatino, 37, gave up a lucrative investment banker job in 2003 to become a £30,000-a-year biotechnology researcher at Oxford University.
They divorced in 2006 and a High Court ruling last year awarded her ex-husband £5.8m.
Miss Radmacher appealed against that decision and her lawyer, Richard Todd QC, told a panel of three Court of Appeal judges the freedom to agree a contract was "at the heart of all modern commercial and legal systems".
He said Miss Radmacher had never said her former husband would leave the marriage with nothing.
The Court of Appeal judges ruled that Mr Granatino's pay-out of £5.8m should be cut to about £1m as a lump sum in lieu of maintenance.
In addition, there will be a fund of £2.5m for a house that will be returned to Miss Radmacher when the younger of their two daughters, who is six, reaches the age of 22.
Mr Granatino's debts, of about £700,000, are also to be paid off by the heiress, who had always agreed to this part of the settlement.