The actress - who plays Claire Bennet in the hit series which is being shown on BBC2 - will appear in new print ads next month, which were shot by famed photographer Annie Leibovitz.
Panettiere, who celebrated her 18th birthday last week, wears a red dress and the famous milk moustache in the commercials, which show her holding an exploding glass of milk, accompanied by the slogan: "You don't have to be a hero to feel invincible. That's why I drink milk."
She joins an elite list of celebrities including Britney Spears, David Beckham, and Beyonce who have fronted the campaign to encourage youngsters to drink three glasses of low-fat or fat-free milk a day.
The actress joked to US chatshow host David Letterman on his Late Show recently about reaching her milestone birthday: "I don't think much changes when you're 18 - maybe the way people treat you.
"But I think the only things I can do is buy cigarettes, porn and, if I get in trouble with the law, I'm kind of screwed."
As well as having a party on the beach, the young starlet also registered to vote.
