Five judges made their ruling at the House of Lords
A judgement in Britain's highest court has been hailed as a "landmark decision on free speech" and a major boost for investigative journalism in this country.
Lawyers say the ruling brings English libel law more into line with that in the United States, where the media have traditionally had greater freedom to write about public figures.
Five judges in the House of Lords overturned two judgments in lower courts requiring the Wall Street Journal Europe to pay £40,000 in libel damages to a billionaire Saudi businessman.
Mohammad Jameel, whose family owns a car dealership in Oxford, had sued the paper over a report that his bank account was being monitored by the Saudi authorities.
The story said he was one of several prominent Saudis whose financial affairs were being examined at the request of United States agencies, to ensure no money was channelled - intentionally or unknowingly - to support terrorists.
The paper argued in its defence that the story showed how strongly Saudi Arabia was working in the fight against terrorism.
It said printing the story was in the public interest, even if the allegations turned out to be untrue.
This concept of "qualified privilege" is known as the "Reynolds defence", following a case brought by the former Irish prime minister, Albert Reynolds, against Times Newspapers in 1999.
The five law lords unanimously decided the Wall Street Journal story was in the public interest.
If ever there were a newspaper story which met the test it was this one, Lady Hale said.
"We need more such serious journalism in this country and our defamation law should encourage rather than discourage it," she said.
Lord Hoffmann said: "The thrust of the article as a whole was to inform the public that the Saudis were cooperating with the US Treasury in monitoring accounts.
"It was a serious contribution in measured tone to a subject of very considerable importance."
The key words are "serious" and "responsible", says Mark Stephens, of the law firm Finer Stephens Innocent, who represented the Wall Street Journal in the case.
"This is a decision which will free responsible investigative journalists from threats of libel," he said.
But he said the public-interest defence would not protect kiss-and-tell "celebrity lover" stories.
Most previous attempts to apply the Reynolds defence have failed, so the judgment will give heart to those journalists and lawyers who have sought its protection.
In July, a leading British book publisher warned of the 'chilling effect' the law would have on journalism, after a judge rejected its defence of qualified privilege in a libel action brought by a former police officer.
The case was brought against Orion Publishing and the author Graeme McLagan, a former BBC home affairs correspondent, over their book 'Bent Coppers'.
In a statement, Orion Publishing said it was "extremely surprised and disappointed" that its case had failed.
"The book Bent Coppers is a serious investigative work covering matters of major public concern" it said.
"If this judgment stands it will have a chilling effect on the ability of authors to write, and publishers to publish, comparable books in future.
This will in turn have a damaging effect on freedom of debate in this country."
It remains to be seen whether this libel judgment - like the ones against the Wall Street Journal - will be overturned.