The Scot has been selected for the initial eight-man squad for the men's road race – he became eligible last month after the British Olympic Association were forced to drop their lifetime ban for doping offenders.
Millar was banned for two years in 2004 after admitting to taking the blood-boosting agent EPO. Since then, he has become a leading campaigner against drugs.
He said: "For eight years, I'd been through it all – bans, sanctions, being ostracised, legal problems – and the only thing left to hang over me was my lifetime Olympic ban and I didn't realise how much I hated living with it until it was actually lifted.
"It was like taking off the final handcuff."
Millar's inclusion – like that of sprinter Dwain Chambers, another reformed drug cheat – has been widely questioned, with four-time gold medallist Sir Chris Hoy particularly vocal in his support of a lifetime ban from the Games.
Although track racer Hoy has pledged to give his team-mate 100% backing following Wednesday's squad announcement, Millar appears unimpressed.
He said: "I understand completely his position. He's this paragon of perfection. He lives in a white world.
"Perhaps some of us live in a bit more of a grey world where we understand what actually goes on a bit more.
"However. we need people like Chris. Redgrave's another. Sir Chris Hoy, Sir Steve Redgrave: they are white knights."