Dylan is the half-human son of Gwen and William Piper. Through his mother, he is the grandson on Agatha Cromwell, and is a warlock capable of performing magic. Unlike his two sisters, Marnie and Sophie, Dylan doesn't like to use magic, but will make exceptions to assist his family and further his studies. Dylan is something of a nerd, as he prefers to study more than anything.
In Halloweentown, Dylan is at home with his family on Halloween Night; much like his mother, he is shown to dislike Halloween and the supernatural. However, Dylan's grandmother, Agatha arrives and encourages Dylan and his sisters in Halloween traditions. Later that night, Dylan is woken up by Marnie, who has overheard a conversation between Gwen and Agatha that revealed that both women were witches from a town called Halloweentown. Marnie learned that she had powers as well, and decided to follow Agatha to Halloweentown. Dylan follows reluctantly.
The three siblings eventually meet up with Agatha, and learn of Halloweentown's recent troubles, which include the mysterious disappearances of citizens. By this time, Gwen has arrived to take her children home, but finds that the bus isn't running. Dylan suggests meeting with the mayor, Kalabar, stating Kalabar to be a helpful person. Kalabar promises to help, but quickly leaves to handle an emergency. Dylan and his family then spot Agatha going to an abandoned theatre, and choose to follow. A shadow creature appears and quickly stuns both Agatha and Gwen, leaving Dylan and his siblings to return them to normal. Marnie and Sophie are able to use their magic to light a magical talisman.
Dylan and Sophie hide in the town square while Marnie attempts to install the talisman; both are surprised when the shadow creature arrives and reveals its true identity as Kalabar, who attempts to incite the citizens to take over the human world. Luckily, Marnie is able to use the talisman to reverse Kalabar's previous spells. Gwen, Agatha, and Marnie attempt to confront Kalabar but their combined strength isn't enough. In his anger, Dylan activates his own magic, much to his surprise and mild disappointment. However, he combines his magic with the rest of his family to defeat Kalabar. The family then returns to the mortal realm, with Dylan attempting to find a logical explanation for his powers.
In Halloweentown II, Dylan retains his reluctance to be involved with magic. Though he attempts to reach out to girls, his efforts are usually rebuffed due to his apparent nerdiness. On Halloween night, Marnie and Agatha travel to Halloweentown to discover the cause of an apparent Gray Spell that is turning Halloweentown's creatures into bland human stereotypes. While there, they contact Dylan to find a spell from Agatha's spellbook, but Dylan finds that the book has been stolen. It is soon discovered that Kalabar's son Kal, posed as a human to steal the book.
Meanwhile, Gwen travels to the school's Halloween dance with a man named Alex; in reality Alex is a frog golem created by Kal to distract Gwen. Dylan and Marnie realize this, and travel to the school to stop him, reluctantly on Dylan's part. Both kids have a hard time convincing Gwen, until Sophie causes Alex to demonstrate frog-like behavior. After learning of the Kal's potential plans, the group splits up to look for him. However, Dylan and Sophie are soon forced to content with Kal's plot when Kal transforms all the humans into creatures, including Gwen. By this time, Agatha and Marnie are trapped in Halloweentown, as the portal between the world's is closed. Marnie, Luke, Dylan and Sophie are able to combine their abilities to forcibly open the portal. Marnie confronts Kal and Kal's plans are stopped.
Dylan then goes to Halloweentown, and is reluctantly convinced to use magic to reverse the effects of the Gray Spell.
In Halloweentown High, he doesn't use his powers at all and falls for a girl before finding out she was a pink troll. Though he doesn't use magic at all in this movie, he states that he has tried to apologize to Natalie using magic to speed-up the speaking process.
In Return to Halloweentown, he attends Witch University with his sister, and confesses that he used his powers to study rapidly in high school, which is the reason to why he skipped a grade and is able to attend college with his sister. He also falls for the evil Sinister sisters but they use him to get the Gift - his family heirloom, so they can try to take over Halloweentown. Later he becomes the wielder of the Gift but decides to hide it in a book. He ends up using a magic a few times in this movie: he speed-reads in order to get the information on Splendora, admits to using it in high school and uses it to help "destroy" the Gift as it takes three Cromwells to do and only he, Gwen and Marnie were around.