Marnie Piper is the eldest daughter of Gwen and William Piper, grandaughter of Aggie, and older sister of Dylan and Sophie. She is the main protagonist of the Halloweentown series, a young witch who has always loved the holiday of Halloween. Marnie is 13-years-old in Halloweentown, 15-years-old in Halloweentown II: Kalabar's Revenge. She is pretty and headstrong individual, especially when it comes to magic. Like her grandmother and her sister she has a sixth sense or precognition power as well as being an expert bromstick flyer. She is the character who uses magic as much as she can but also cares about it and tries very much to save Halloweentown and her magic

This is the only role that had to be recast, with Kimberly J. Brown playing the role from Halloweentown to Halloweentown High, and Sara Paxton in Return to Halloweentown.