Justin Harper was Piper Halliwell's classmate and friend from high school. He had a one-sided crush on Prue back in school and followed her around, but they never dated until they ran into each other at Piper's high school reunion ten years later.
Justin met the sisters and Leo while driving around his old neighborhood and stopped at the manor. Piper was happy to see him, to which Leo responds a little jealous until Prue assured him that Justin had a crush on her all through high school. However, when asked to help bring some food to P3, Justin acted like he didn't remember Prue, calling her Phoebe instead.
Later at the club, Justin stopped Prue from coming to Piper's defense against Missy Campbell, another former classmate. Justin told her that Piper needed to learn to stand on her own and how Prue once finished a speech for her in high school. Prue then realized that Justin had pretended not to remember her before. Justin explained that she plagued him in high school, because she ignored him, and that he had learned not to date women like her anymore. Justin then told her that, much like Prue herself, he makes lists about everything and they started comparing lists. Prue became more interested in him when Justin revealed he believed in the supernatural.
At the reunion, Justin helped Prue and Phoebe carry a possessed and unconscious Piper to the car, while under the impression that Piper was drunk. When the sisters return to the club after saving Piper, they find Justin still there waiting for them. He asked what happened and Prue assured him that she would tell him all about it once he called her.
After dating for a while, Justin invited Prue to his family barbecue. Prue decided not to go due to the relationship still being in the flirty banter stage. However, Phoebe suggested that she was avoiding it because it was a big family gathering, due to her issues with their father.
Prue and Justin had been dating for a couple of weeks, but Prue admitted she was starting to lose interest. Compared to her magical life, Justin was too predictable and not mysterious enough for her. After ending a date at P3 early, they made plans for lunch the following day. This was overheard by the shapeshifting warlock Zile, who intended to marry Prue in a dark ritual to turn the Power of Three evil and add their power to his.
The following day, Zile called Prue, pretending to be Justin, and asked her to meet her at the restaurant. Having shapeshifted into Justin, Zile proceeded to seduce Prue into kissing him, which paralyzed her and teleported both of them to the lair of the dark priestess, Dantalian. There, Zile assumed his true form and asked Dantalian to perform the wedding ritual. Meanwhile the real Justin ran into Phoebe at the manor, which led Phoebe and Piper to realize Prue was kidnapped.
The dark priestess Dantalian married Zile and Prue in the dark ritual. This affected both Prue and her sisters, turning them into evil warlocks. Once Zile was vanquished by the sisters, they once again turned good and vanquished Dantalian. However, the seduction of evil made Prue realize that Justin was just too boring for her and she broke up with him.
- Justin is Prue's last boyfriend on-screen.
- Like the sisters, Justin is another alumni of Baker High School. He was in the same year as Piper and had a one-sided crush on Prue.
- It is presumed that Justin used to live close to the Halliwell Manor, as he said he was driving around the old neighborhood when he ran into the sisters in their street.
- He was possibly the last stable relationship Prue had with.
Justin Harper appeared in a total of 2 episodes over the course of the series.