Robin Ackroyd, a freelance journalist who wrote an article about the treatment in hospital of moors murderer Ian Brady, has won his right to protect his sources after a gruelling and costly seven-year legal battle with the Mersey Care NHS Trust.
The National Union of Journalists, which has supported him throughout, has hailed the "landmark victory" at the Court of Appeal.
NUJ general secretary Jeremy Dear said: "At last justice has prevailed and Robin Ackroyd - and all journalists - can rest assured that they will not be forced to reveal their sources."
The NHS Trust could appeal against the decision.

An anonymous marriage proposal in an advert on the front page of the Stroud News & Journal remains a mystery.
Editor Sue Smith received an envelope stuffed with £300 and an anonymous covering letter asking for an attached notice to be placed in the paper on Valentine's Day "as big as possible for £300".
Sue said: "We were waiting on tenterhooks but we've had no response at all. We thought someone might get in touch after it appeared - it is a lot of money to fork out for no response."

Johnston Press chief executive Tim Bowdler will be among the speakers at the inaugural MediaFinance 2007 conference, which is being held in London on May 9.
The event will bringing together leadership from across the media with investors and other intermediaries to discuss the key financial and strategic issues facing the media businesses of tomorrow.
It will examine key trends in media such as consolidation, cross-border deal making, diversification and the rise of private equity interest in media.

Archive copies of The Sentinel stored at libraries in Staffordshire are to be made available on DVD.
Until now visitors have been able read copies of the newspaper dating back to 1854 but could only access the records by microfilm.
The new DVDs will be available to view at both Hanley and Newcastle libraries.