He broke the story that destroyed a 168-year-old newspaper, humiliated one of the world's most powerful media moguls and cast a spotlight on a phone hacking scandal that has embroiled politicians, police and journalists.
And he says there is more to come.
Guardian journalist Nick Davies spent years investigating phone hacking claims in the face of police indifference and ridicule from rivals.
"It's a great story about the abuse of power," Davies told The Associated Press. "That's what all journalists want to expose, isn't it? The abuse of power."
It all began in 2005, when the News of the World tabloid published a story about Prince William suffering a knee injury.
Royal household staff believed the paper, part of the Rupert Murdoch media empire, could only have known about the injury by listening to the prince's messages, and they asked police to investigate.
The inquiry led to two men working for the News of the World: reporter Clive Goodman and private investigator Glenn Mulcaire.
They were jailed in 2007 for eavesdropping on messages left on the mobile phones of royal aides, including some from Prince William and his brother Harry.
The tabloid's editor, Andy Coulson, said he knew nothing about the men's actions but still resigned.
Soon after, then-opposition leader David Cameron hired Coulson as his communications chief.
Mr Cameron kept him on when he became Prime Minister in May last year.
Although interest faded in the story, Davies stayed on the trail.
Suspecting the practice of phone hacking was more widespread, Davies turned to sources he had cultivated during some 30 years at The Guardian.
The Guardian ran his piece in 2009. It revealed that Mr Murdoch's papers had paid out more than £1 million to settle lawsuits involving allegations of hacking into phone messages, as well as illegally accessing tax records, social security files and bank statements of politicians, actors and sports stars.
Davies said police had evidence that thousands of people - from celebrities such as Gwyneth Paltrow and Sienna Miller to politicians including former deputy prime minister John Prescott - had been targeted by private investigators working for Murdoch papers.
He said court papers showed a suit brought against the News of the World by Gordon Taylor, chief executive of the Professional Footballers' Association, was settled in exchange for a gag order preventing Taylor from talking about the case.
It was not until last week, however, that the scandal exploded with Davis's revelation that the News of the World had hacked into the phone of a 13-year-old murder victim, Milly Dowler, and may have impeded a police investigation into her 2002 disappearance by deleting some messages.
Until then, the public believed the phone hacking scandal affected only celebrities, sports stars, politicians and the royal family - powerful people who needed no help in battling the British tabloids.
But the idea of reporters listening in to messages left for a murdered schoolgirl proved too much.
Mr Cameron, who had once defended Coulson, was forced to distance himself from him.
Mr Murdoch's British company, News International, shut down the News of the World, saying the paper had become too toxic to survive. Police officers, too, offered up a series of apologies for not investigating earlier.
And on Wednesday, Murdoch withdrew his bid for control of satellite broadcasting behemoth British Sky Broadcasting after Mr Cameron joined opposition parties in opposing the takeover.
"When I wrote the story about Milly Dowler, I sent an email to [my] editor saying I think this is the most powerful story so far. But I did not foresee the extent of the emotional impact," Davies told the AP.
"It was almost unreal to watch ... The Prime Minister, who had been so close to Murdoch and keen to defend the BSkyB and defend Coulson suddenly flipped his position."
Davies has also clashed with WikiLeaks founder Julian Assange, whom he persuaded to work with The Guardian in releasing WikiLeaks material.
The two men later fell out after Davies reported that Swedish police were investigating allegations that Assange sexually assaulted two women.
Some of Assange's supporters criticised The Guardian for running the story against such a key source, but Davies says that is how journalists become corrupt - by staying away from stories about people they are close to.
Davies says his latest reports about the hacking scandal are only the beginning.
"There are still ways this story can expand its scope," he said. "The story may expand to other newspapers and other techniques for getting information. And it could well expand to other countries."
AP