Millar, team-mate to Lance Armstrong as a teenager, a Tour de France star on his debut in 2000, but banned for doping in 2004, is now cycling's repentant anti-doping talisman, a WADA (World Anti-Doping Agency) committee member and a long-standing critic of cycling's governing body, the UCI.
Now he is supporting his Garmin-Sharp team-mates, Christian Vandevelde, David Zabriskie and Tom Danielson, who were among those who confessed to doping and gave sworn affidavits of Armstrong's excesses to the investigation by the US Anti-Doping Agency (USADA) .
"They're humiliated, embarrassed and frightened – all of that. Their lives will never be the same again. It's going to be very hard for them. I know it will."
Millar is painfully aware of what he calls the "psychological damage" of doping.
"People die from doping," he said. "The most infamous deaths have been through the psychological damage that doping causes. I don't think I could have ever gone that far, but I have a lot of empathy for those who did. Doping wreaks havoc on your mental health. Some guys can handle it, others can't. I was lucky, people who loved me helped me through it."
Millar believes it is right that Vandevelde, Zabriskie and Danielson only face six-month bans. "By doing what they have, they have changed the sport for the better," he said. "There are plenty of other guys breathing a sigh of relief, hundreds of guys whose names have not been mentioned."
Millar was aware that several of his team-mates, and former professional Jonathan Vaughters, now Garmin-Sharp manager, were being asked to give evidence against Armstrong by USADA.
"I knew it was going on," Millar said. "I never spoke to Christian about the details of what he said to USADA, although I knew his history. But Jonathan had made it clear to the guys that they had to tell the truth and that the team would stand by them.
"That was an admirable thing to do. And our sponsors have always known about our history and that of our riders. We have always been honest. They've bought into the idea that the sport can change if people are transparent about their past."
Millar also dismissed the idea that telling the truth would kill the commercial health of the professional scene. "Not in the long term, because if you're honest about the past and about the sport, then it's possible to still attract sponsorship."
Millar believes that doping was so endemic that the majority of those involved in cycling aged over 35 would have experienced the sport's doping culture.
"It's a sad truth," he said. "That's why Team Sky's zero tolerance doesn't work."
Despite Team Sky principal Dave Brailsford's repeated assertions that nobody with any doping connections would be hired by the team, former Sky rider Michael Barry was among those to confess and give evidence against Armstrong.
The British team are now coming under pressure to clarify the exact nature of team manager Sean Yates's long standing relationship with Armstrong.
"Sky have shown a certain amount of naivety," Millar said. "We have to live with our history and understand it. But Sky have an opportunity here and maybe they should acknowledge that it was a bigger problem than they knew. They're sticking to the idea that it's better to not talk about it, but I don't think that works."
Like many, Millar has welcomed the blood-letting of the past few days. The truth about Armstrong's seven Tour wins has, almost, washed the streets clean, but it has also wrecked professional cycling's image.
"That's the feeling now," he said. "How did they think they could get away with it? We all knew it was coming out. But even, so it's hard on the young guys competing now who weren't part of it all. I know that some of the some young French riders wanted it all left alone, because of the stigma they would face.
"I've always believed the sport would clean up, I'm an example of that. I said it would take 10 years because of the generational shift, but it's hard for the young guys right now."
Arrested by the French drugs squad in 2004, Millar was one of the first riders to break cycling's law of silence. "People say why didn't the pros at the time stand up, but how could you ever have said anything when everybody – the other riders, the media, the UCI – ignored you? If you spoke out, you were isolated. Look at what happened to the handful that did. That's the power of the omerta. That's not the case any more.
"The majority of people wanted to believe in Lance, some emotionally, others because of commercial reasons. That's why I've got so much respect for what USADA have done, for the detail they have gone into. That was what was needed to really make it convincing."
Recently Millar took the decision to confront the UCI over their shortcomings when he publicly criticised UCI president Pat McQuaid during a press conference at the World Road Race Championships in Holland.
"He could have turned around public opinion, people really wanted to hear him say positive things, but I sat there thinking, 'My God, we're going backwards'. It was really hard. It made me very angry and frustrated. I sat there wondering 'do they even care?'
"We're all culpable for this. But the UCI flatly deny it and refuse to be accountable. It's obvious they knew what was going on. That's evident from the 50% hematocrit test [introduced by former UCI president Hein Verbruggen, which did not test for EPO but measured riders red blood cell levels]. They introduced that because they knew there was a massive problem in the sport.
"Why didn't they go public at the time? Why didn't they say there was a massive doping problem in the sport? Instead they said it was all made up by disenchanted riders and journalists looking for scandal."
Millar thinks McQuaid will survive the scandal. "That's how the UCI is, but I don't think Verbruggen [currently the UCI's honorary president] has the right to survive."
Yet, after the most torrid episode in his sport's history, Millar believes there are grounds for optimism.
"The sport has got better since McQuaid came in, but he has to break free of Verbruggen," he said. "I don't think the UCI are doing a bad job now, they're at the forefront of anti-doping but they're self-sabotaging by not dealing with the past. This is Pat's moment. Now it's up to him."
o Jeremy Whittle is author of Bad Blood: The Secret Life Of The Tour de France