Barry George, the man serving a life sentence for the murder of BBC TV presenter Jill Dando, has won the right to a fresh appeal.
Barry George has always denied he murdered Miss Dando
The Criminal Cases Review Commission said it would refer the case back to the Court of Appeal.
It said too much weight had been placed on forensic evidence concerning a speck of firearms residue in the trial.
George was convicted in 2001, two years after the BBC presenter was shot dead on her doorstep in Fulham, west London.
A convicted sex offender, 47-year-old George was jailed for life.
He has always denied the murder and in 2002 he took his case to the Court of Appeal for the first time and lost.
At his trial, the jury heard that he was a near neighbour, a loner and obsessed with guns, celebrities and the BBC, where he had worked as a messenger in 1976.
He was found guilty by a majority verdict of 10 to one after the Old Bailey jury heard forensic scientists had found a single speck of residue from the gun used to kill Miss Dando, 37, in the pocket of his coat.
George's solicitor says the original case against him placed too much importance on this piece of evidence and appealed to the commission on those grounds.
Jill Dando, the "Golden Girl" of television
It is the commission's job to consider whether, with new evidence or argument, there is a real possibility that a conviction would not be upheld.
Chairman of the commission Professor Graham Zellick told BBC News: "We have reached the conclusion that the weight placed on that evidence at the trial, and presumably by the jury, was inappropriate, was incorrect."
The case, he said, would now go before the Court of Appeal once a date could be fixed.
He said he had been asked to consider other issues but the case was not referred to the Court of Appeal on any other grounds.
George's solicitor Jeremy Moore said he and his client were "very pleased" by the decision and would now begin to prepare for Court of Appeal proceedings.
"Mr George has now spent seven extremely difficult years in custody for a conviction which we believe that, in the fullness of time, will be seen as one of the gravest miscarriages of justice of recent years," he said.
In a statement, Jill Dando's brother, Nigel, said: "I note with interest the decision of the Criminal Cases Review Commission. Because this matter will now return once more to the Court of Appeal, I think it is better to make no further comment at this stage."
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
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
Earlier, Mr Moore said there was now fresh evidence which suggested George's coat may have been contaminated through the air, rather than by a firearm.
George's lawyers have previously argued his coat may have been contaminated with gunshot residue by armed officers involved in his arrest.
Police have always denied any of the arresting officers were armed but Mr Moore says there are new witnesses able to contest that.
Before George was found guilty, some thought the murder might have been the work of a professional hit man or an obsessive fan.
Described as the "Golden Girl of television", Miss Dando presented BBC programmes including the Six O'Clock News, Breakfast News, Crimewatch and Holiday.