(CNN) -- It cost his newspaper a thumping $1.6 million in legal costs.
He was the subject of vilification from both cycling fans and officials -- not to mention from a man who had become a global sporting icon.
But not once did David Walsh waver in his quest to unveil the truth about Lance Armstrong and his doping lies -- despite the almost insurmountable obstacles placed in his way.
"People find this strange, but for me it was the time of my life," Walsh told CNN's Changing Gear series in an interview before the start of the Tour de France.
"I loved it. I thought 'This was journalism, this was what our game was about' -- asking questions that people didn't want to answer was actually the life blood of journalism for me at that time."
The award-winning Sunday Times journalist spent 13 long and sometimes lonely years pursuing Armstrong.
Labeled a "Little Troll" by the American, Walsh was finally vindicated when the disgraced cyclist confessed earlier this year.
It was Walsh's finest hour and he even gained an apology from Armstrong during the course of the Texan's televised interview with Oprah Winfrey earlier this year.
But the 58-year-old Irishman did not feel any sense of real elation -- only the satisfaction of a job well done.
"For me, it wasn't a conclusion that was thrilling, or exciting, or interesting -- it was the chase," said Walsh.
"I've used the expression that the hunt was better than the kill, and it very much was. I loved getting new information about Armstrong."
Back in 1999, when the world was in thrall to the cancer survivor after Armstrong's remarkable comeback to win the Tour de France that year, Walsh was immediately skeptical.
"It was perfectly obvious to anybody with half a brain that Armstrong was cheating," said Walsh.
"We were told this is a clean Tour, but it was the fastest in history -- completely illogical!"
Armstrong's treatment of the French rider Christophe Bassons, who was renowned for his anti-doping stance, only served to further raise Walsh's suspicions.
"I mean, Armstrong bullied him, most of the peloton bullied him and I thought: 'If you were anti-doping, that's not how you would treat somebody who clearly was riding clean.'"
It was the start of a crusade to uncover the truth, though at first nobody wanted to listen.
In the aftermath of the 1998 Tour de France -- blighted by doping, with police raiding teams to find illegal products -- cycling had been desperate for a good news story and was prepared, in Walsh's words, to "suspend disbelief."
"An American guy comes from Texas, single-parent family, he's come through life-threatening cancer, he's in the lead," explained Walsh.
"It's a story that could take the Tour de France from its knees and put it standing up again and the race organizers embraced that."
As Armstrong's winning run continued -- eventually to total an unprecedented seven Tour wins in a row -- so in Walsh's view the American's web of deceit grew and he alleges others were complicit in the cover up.
Walsh was determined to publish his version of events and when LA (Lance Armstrong) Confidential hit the bookshelves in 2004 and a story based on it was published in the Sunday Times, the libel suits and the threats intensified.
Walsh was at an explosive Tour media conference later that year and Armstrong, when inevitably asked about the book, singled him out, as the journalist vividly recalls.
Armstrong said: "Well as the esteemed author is here, I will answer this.
"And then he said 'Extraordinary allegations, no, extraordinary accusations must be followed by extraordinary proof.' Everybody thought that was a great one-liner."
Walsh had based his book on interviews with Betsy Andreu, the wife of cyclist Frankie Andreu, a former teammate of Armstrong, Emma O'Reilly, who had acted as personal masseuse for the now disgraced cyclist, and a former teammate from the 1990's, Steven Swart.
When details of the systematic doping carried out by Armstrong and his team finally emerged in a report by the United States Anti Doping Agency (USADA) in 2012, it vindicated the whistleblowers' stance -- as well as Walsh and his co-author Frenchman Pierre Ballester.
But back in 2004, with Armstrong at the peak of his fame, it was inevitable he would challenge such damaging revelations to protect his reputation.
The Sunday Times stood by their man and his story, but when libel action in the UK courts was commenced by the litigious Armstrong, they knew the outcome would probably be in the American's favor.
Walsh recognized the seriousness of the situation, but admitted his judgment became clouded.
"I'm there saying 'Well I don't care, I just want this stuff out there.'
"And I wasn't seeing reason to be honest. I would have been a bit of a nightmare from the legal department's point of view and they were right.
"It did cost the Sunday Times a million pounds, but the newspaper were tremendously supportive as was my sports editor," added Walsh, referring to the out-of-court settlement reached with Armstrong in 2006.
By then the Texan had retired from the sport for the first time, though the rumors would not go away.
Walsh believes that cycling's governing body -- the International Cycling Union -- bears a heavy responsibility for not cleaning up its own sport in the face of overwhelming evidence of doping, not just by Armstrong but other leading riders.
He is heavily critical of its chiefs past and present, Hein Vergruggen, who resigned in 2005 to be replaced by Pat McQuaid.
"They were the people whose ultimate responsibility it was to ensure that the riders riding clean were protected. They didn't do their job," said Walsh.
"McQuaid said he was very anti-doping, but he didn't want to find out the truth about Lance Armstrong. He wanted basically, to sweep it under the carpet, and in my opinion, his organization now cannot have any credibility as long as he's president."
Walsh's fellow Irishman McQuiad has a different perspective.
"Hindsight is an exact science and hindsight is 20-20 vision," McQuaid told CNN as part of the Changing Gear series. "Of course you would do things differently but that doesn't mean that I regret anything that I did.
"Many, many federations around the world told me that under no circumstances should I contemplate resigning," added McQuaid defiantly.
McQuaid is being challenged for the top job at the UCI by British Cycling's Brian Cookson, and Walsh, while not specifically backing any candidate, is convinced a change is urgently needed.
"I have been saying this since the whole controversy unfolded -- the people who were in charge during this fiasco, shouldn't still be there.
"If cycling could find a credible candidate within its own ranks to take over from Pat, it would immediately change the perception of the UCI and people would say 'You know what? Let's give this new guy a chance.
"And let him reassure us that anti-doping really is going to be the number one item on the agenda."
Armstrong came out of retirement in 2009 to ride for the Astana team and finished third in that year's Tour de France. He raced two more years with Team RadioShack with diminishing success before quitting in early 2011.
By then he was the subject of a U.S. federal investigation into doping allegations and more former teammates, notably Tyler Hamilton and Floyd Landis, came forward to specifically implicate the Texan as the ringleader.
Once again, Walsh had been ahead of the game, having published From Lance to Landis: Inside the American Doping Controversy at the Tour de France in 2007.
The federal case against Armstrong was eventually dropped, but the U.S. Anti-Doping Agency persisted in its investigations.
Grilling his former teammates and other close connections, the USADA formally charged Armstrong in June 2012 with using illicit performance-enhancing drugs in "the most sophisticated, professionalized and successful doping program that sport has ever seen."
Walsh, who has won a string of press awards, was finally vindicated as he recounts in his book Seven Deadly Sins: My Pursuit of Lance Armstrong.
For the first time since 2004, Walsh will cover the Tour de France after Britain's Team Sky Cycling team, who won the Tour last year with Bradley Wiggins, gave the journalist exclusive behind the scenes access to the 2013 race.
"I'm really looking forward to it, but I'm looking forward to it because I feel that the Armstrong era has been dealt with and we can start again," said the Irishman.
"We can start tentatively believing in some of what we see, and that's why I'm back."
Not that Walsh believes the doping culture in cycling has been completely eradicated and points to last year's race where Luxembourg's Frank Schleck fell foul of the testers.
"The one certainty is that Frank Schleck wasn't the only guy who doped in last year's Tour de France," said Walsh. "That's absolutely certain.
"Nobody of sane mind would believe that the people who get caught are the only people who dope."
Walsh has spent four weeks in total with Team Sky as they prepared for this year's Tour where Chris Froome, second last year to Wiggins, who will be absent this time, is regarded the favorite.
The journalist has had to soak up some criticism on Twitter that he has become a "PR agency for Sky" but Walsh remains unabashed.
"They say they're clean. I've seen nothing to make me suspicious that they're telling a lie when they say they're clean, though that doesn't mean that things couldn't be happening behind my back.
"The conclusion I've come to given the time I've spent with them is that they certainly don't have an organized doping program within the team."