She is best known for the role of Piper Halliwell in the series Charmed.

The daughter of David and Laurelei Combs, who gave birth to her at the age of sixteen and was married to her father for two years (1973–1975). She moved with her mother to New York at the age of eight and soon began appearing in print and television commercials. She studied at the Professional Children's School N.Y. under Ernie Martin.

Holly's mother dreamed of becoming an actress, but breaking into show business was not easy at all, so she worked as a waitress and a model, since someone had to pay their bills. When Holly was twelve, Laurelei married for the second time. Holly's stepfather was a bartender, so the family's financial situation did not change. "We lived in such cramped conditions!" Holly recalls. "The only place where you could be alone was the bathtub." Thanks to these "cramped" relationships, Holly embraced her mother's ideas and decided to become an actress.