Pettyfer was born in Stevenage, Hertfordshire, England. He is the son of Lee Ireland, an interior decorator, and Richard Pettyfer, an actor. He has a younger half-brother, James Ireland who is a junior tennis player.
He began his career as a child fashion model at the age of seven, for Gap, after meeting Ralph Lauren in a toy store in New York. He also did advertisements for some yogurt brands. His first commercial was at age six. After his GCSEs, he left Shiplake College to attend the independent Sylvia Young Theatre School in London. In June 2005, he was cast in his most prominent role, that of teenage MI6 spy Alex Rider in the film Stormbreaker, based on the novel by Anthony Horowitz. He was one of 500 who auditioned for the role. Pettyfer will not reprise the role if there is another Alex Rider film because he is now too mature for the role. In 2011 he starred in the film, Beastly, based on the novel by Alex Flinn, alongside Mary-Kate Olsen, Vanessa Hudgens, and Neil Patrick Harris. Another prominent role includes Alex’s key role in Magic Mike.
Pettyfer and Dianna Agron, who incidently played his on screen love interest Sarah Hart, had a relationship which ended in February 2011. He was reportedly engaged to actress Riley Keough, Elvis Presley's granddaughter, whom he met on the set of their movie, Magic Mike.