Ian Edmondson, 45, pleaded guilty at the Old Bailey to conspiring with private eye Glenn Mulcaire and NotW colleagues to hack a host of celebrities, sports personalities, politicians and even royalty between 3 October 3 2000 and 9 August 2006.
The journalist had been dropped as a defendant in the original hacking trial of ex-editors Andy Coulson and Rebekah Brooks in December last year, after the trial judge deemed him "unfit" to continue.
His guilty plea came as he faced a re-trial at the Old Bailey since Justice Saunders had deemed him "fit" again in July, it can now be reported.
During the original eight-month trial, jurors were told how Edmondson had worked as an executive on the newsdesk - the "engine room of the newsroom" - since 2005.
He was suspended in 2010 after three emails emerged implicating him in the hacking conspiracy and he was sacked for "gross misconduct" a year later.
After he joined the now defunct tabloid, Edmondson had been keen to terminate Mulcaire's £100,000 a year contract, but in 2005 he signed off its renewal once he realised its value, the court heard.
In all, he was responsible for 23.9% of the newsdesk orders to Mulcaire, including ones relating to Tessa Jowell, Freddie Windsor and Lord Prescott, according to an analysis of detailed notes kept by the private eye.
In 2006, he received an incriminating email from Coulson ordering him to "do his phone" in an apparent reference to the celebrity Calum Best.
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At today's hearing, prosecutor Mark Bryant-Heron QC outlined how Edmondson had become involved in the "systematic phone hacking" at the NotW.
He said: "There was an aggressive news-gathering culture. The ends seemed to justify the means to get the story in an extremely competitive market."
In his role on the newsdesk, Edmondson not only tasked Mulcaire to hack phones, he also passed on details including mobile phone pin numbers to colleagues to phone hack, and even accessed voicemails himself.
Police found more than 8,000 tasking notes at Mulcaire's home, many of which did not identify who had instructed him. However, 334 of them had "Ian" written in the top left-hand corner, identifying Edmondson as the tasker, starting from February 2005.
Phone records show that between July 2005 and August 2006 there were 900 calls and texts between Mulcaire and Edmondson, demonstrating their "close working relationship", Bryant-Heron said.
The three emails revealing Edmondson's taskings for stories on Jowell, Lord Windsor and Lord Prescott in April 2006 led to the launch of the police investigation into phone hacking, codenamed Operation Weeting.
But his involvement went further, the court heard. He was also copied into emails discussing hacking target Gordon Taylor, chief executive of the Professional Footballers' Association in 2005.
And he was involved in stories about actors Sienna Miller, Jude Law and Sadie Frost as well as singers Sir Paul McCartney and Kerry Katona which all came from phone hacking.
Defending, Sallie Bennett-Jenkins QC said: "Mr Edmondson was aware of phone hacking that was industry-wide and common knowledge.
"Mulcaire had bragged on many occasions in the past of his ability to hack phones and obtain information through that methodology."
She told the court that her client was working "under the direct instruction from senior executives to use Mulcaire".
But Mr Justice Saunders warned him that he could face jail despite admitting his part in the conspiracy.
Adjourning the sentencing for reports on a date to be fixed, he remanded the married journalist on conditional bail but repeatedly cautioned him "not to read anything into that".
Edmondson, of Raynes Park, south-west London, wore a dark suit and tie and sat in the dock with his head bowed, wringing his hands his lap throughout the hour-long hearing.
Following the trial, Coulson, 46, was found guilty of the hacking plot while Brooks, 46, and retired managing editor Stuart Kuttner, 74, were cleared of any wrongdoing in July.
Other NotW journalists had pleaded guilty to being part of the voicemail interception conspiracy before the trial started.
Reporter Dan Evans, 38, of Kilburn, north London, was handed a 10-month jail term suspended for 12 months plus 200 hours of community service.
News of the World news editor Greg Miskiw, 64, from Leeds, and chief reporter Neville Thurlbeck, 52, of Esher, Surrey, were each jailed for six months.
News editor James Weatherup, 58, of Brentwood in Essex, was jailed for four months, suspended for 12 months, and ordered to do 200 hours unpaid community work.
Justice Saunders described Mulcaire, 43, of Sutton, south London, as ''the lucky one'', saying it would be wrong to jail him again after he had already served a sentence in 2006 when he was first convicted of phone hacking with ex-royal editor Clive Goodman.
The judge sentenced Mulcaire to six months imprisonment, suspended for 12 months, plus 200 hours unpaid community work.