Now, 15, and with a movie on the way, Harley has spoken out about what it has been like to grow up alongside the TV character.
Speaking to the BBC, Harley said she went for an audition when she was five-years-old and apparently “sounded like a pig” and got the gig.
"I couldn't read at all and it's a little bit difficult when you've got a five-year-old who's meant to be reading scripts,” she told the publication.
"So all the Peppa guys used to tell me how they wanted me to say the line and I just got used to copying them. So as well as doing an amazing job they were also teaching me how to read as well."
Growing up on the show means her voice has changed, but in a recent interview This Morning, Harley demonstrated how easy it is for her to slip in and out of character.
"[Peppa] has a four-year-old's voice ... my normal voice, I sound like a 15-year-old," she said. "But I can kind of switch between the two now."
This article first published on Practical Parenting.