The bravery of former Watford Observer reporter Sean Hoare helped lift the lid on phone hacking and start the process which saw ex-News of the World editor Andy Coulson convicted, according to one of his colleagues.
Guardian journalist Simon Ricketts praised Sean, who was found dead at his home in Watford in 2011, for speaking out about the "darker side of journalism".
He said he also felt the decision to become a whistle-blower contributed to the fatal deterioration of Sean's health and added he hoped his family would draw some comfort from the court verdict.
Sean was the first journalist to break the silence over phone hacking and named Coulson as someone who "actively encouraged" reporters to engage in the practise when he worked at the now defunct News of the World.
Coulson, who denied all knowledge of hacking at the tabloid, was found guilty at the Old Bailey yesterday of conspiracy to hack phones following an eight-month trial.
Mr Ricketts, who met Sean at the Watford Observer in the early 1990s, said: "Sean was someone who had seen - and participated in - the darker side of journalism. It was clear to me that as time went on, it haunted him.
"His decision to blow the whistle on phone hacking won't have been taken lightly. And I believe the repercussions of that decision contributed to his health deteriorating so very violently and, sadly, ending his life."
"I will always be grateful to Sean for his help and friendship when I started my career as a journalist. His character may have been smeared but his bravery was a key part in opening doors wide on the hacking investigation.
"I hope his family can gain some comfort from the fact Sean's testimony was so important.
"If he were still alive today to hear the verdicts, I think he would have cracked a wry smile and lit another cigarette. That's how he reacted to pretty much every news story."
Andy Coulson, who went on to become David Cameron's director of communications after leaving the News of the World, is now facing a jail sentence after the verdict.
In 2007 he resigned as editor of the News of the World after the paper's royal editor Clive Goodman was jailed for phone hacking.
However Coulson maintained he knew nothing about the illegal practice and said he was standing down because he took "ultimate responsibility" for his reporter's actions.
Then in a 2010 interview with the New York Times Sean contradicted Coulson's denials saying the former editor had openly encouraged staff to hack celebrity phones to beat the competition to exclusive stories.
He told the American paper he was blowing the whistle as he felt it was unfair for all the blame to be heaped on the jailed Goodman, who was described as a "rogue reporter" at the time.
Sean also described how he and Coulson, a onetime close friend, had discussed hacking during their time at the paper and also listened to hacked messages together.
Sean was fired from the News of the World before the interview during a period when he was struggling with alcoholism and drug addiction.
He was found dead at his home in Watford on July 18, 2011, less than a year after the New York Times article was published. The coroner found the 48-year-old died of natural causes but was also suffering from alcoholic liver disease.
An inquest into Sean's death found he used alcohol "as a crutch" to cope with the stress after her blew the whistle on phone hacking.
The coroner was told Sean had done well refraining from alcohol after being diagnosed with the liver condition but relapsed in December 2010 after going public about hacking at the tabloid.