Barry George has won his appeal against his conviction for the murder of BBC TV presenter Jill Dando in 1999.
The Court of Appeal decided the jury's guilty verdict six years ago was unsafe, and has ordered a retrial.
George, 47, was sentenced to life for the shooting of Miss Dando, 37, outside her home in Fulham, west London, but he has always denied his involvement.
The court said new scientific doubts over gunshot discharge residue evidence meant the conviction had to be quashed.
George, dressed in a suit and dark blue shirt, appeared in the dock of the London court as the Lord Chief Justice, Lord Phillips, and two other senior judges allowed the appeal and informed him he would face a retrial.
There was no application for bail and George is to be remanded in custody. Legal proceedings will begin within the next two months.
Outside court, George's sister, Michelle Diskin, appealed for anyone with information about the murder to come forward and said winning the appeal was just "one step" in her quest to free her brother.
"I don't really feel we have victory, we don't have Barry, he doesn't have his freedom yet," she said.
But George's solicitor, Jeremy Moore, said his client was pleased with the result.
He added: "This is only the latest hurdle in what has been a very long road and we now look forward very much to preparing for the trial."
However, Alan Farthing, Miss Dando's fiance at the time of her murder, said: "I am disappointed, particularly for those of us who have suffered the tragedy of losing a loved one prematurely."
JILL DANDO MURDER CASE
26 April 1999 Jill Dando is shot dead in west London
25 May 2000 Barry George, also known as Barry Bulsara, is arrested
29 May 2000 George is charged with murder
2 July 2001 George is found guilty of murder and later sentenced to life in prison
29 July 2002 George loses an appeal against his "unsafe" conviction
16 Dec 2002 House of Lords refuses permission for further challenge
20 June 2007 The Criminal Cases Review Commission grants George the right to another appeal
15 November 2007 George wins a second appeal against his conviction and will face a retrial
George was sentenced in July 2001 to life imprisonment after an Old Bailey jury found him guilty by a majority of 10 to one.
This latest hearing centred on the significance of a microscopic speck of firearm discharge found in George's coat following his arrest more than 12 months after the shooting.
William Clegg QC, for George, argued the firearm evidence carried "zero or neutral evidential weight" and if it was admitted again before a jury, it should have the proper weight attached.
However, Orlando Pownall QC, for the prosecution, told the court that new firearms evidence did not render George's conviction "unsafe" and that it was just one element in a "compelling circumstantial case".
Particle of evidence
Summing up the court's decision, Lord Phillips said the jury in the original trial had been "misled" by prosecutors over the significance of the firearm discharge.
In the appeal, evidence from the Forensic Science Service had shown that it was not right to conclude that the firearm discharge was likely to have come from a gun fired by George, he said.
Magnified 2,000 times: the firearms residue from George's trial
"It was, in fact, no more likely that the particle had come from a gun fired by Barry George than that it had come from some other source," he said.
"The Court of Appeal concluded that, if this evidence had been given to the jury at the trial, there is no certainty that they would have found Barry George guilty.
"For this reason his conviction had to be quashed."
Lord Phillips added that George was one of a number of men who came to the attention of the police in the course of their investigation.
The appeal proceedings began after the Criminal Cases Review Commission (CCRC), which studies potential miscarriages of justice, referred the case to the Court of Appeal.
The three-day hearing was George's second legal challenge over the Old Bailey verdict.
He lost his first appeal a year after his conviction.