Justin was born into an upper middle class Pittsburgh family. His mom's name is Jennifer and his dad Craig, a Dartmouth College-graduate businessman. Craig strongly wishes for Justin to attend Dartmouth, despite Justin's dreams to be an artist.
Justin has a little sister named Molly (who is seen in only two episodes) and his best friend is Daphne Chanders. Justin and Daphne attended highschool together at St. James, a religious private preparatory academy.
In the pilot episode, Brian meets Justin, a virgin, outside the gay club Babylon, and takes him home to have sex with him. Justin is responsible for naming Gus, Brian and Lindsay's biological son. After their encounter, Justin falls in love with Brian and eventually gets Brian to have sex with him again, breaking Brian's own rule of not having sex with the same person more than once. This causes Brian's best friend Michael to become jealous and act hostile towards Justin.
During the first season, Justin's parents struggle to come to terms with his homosexuality, his father kicking him out of the house. He would remain estranged from his father for the rest of the series. While his mother Jennifer takes a little time to understand her son, after a few months she becomes supportive of Justin and becomes involved in PFLAG.
He confides in his best friend Daphne. Late in Season 1, she asks him to be the boy to take her virginity, since he is experienced. He agrees, and she falls in love with him the same way Justin fell in love with Brian. However, Justin shoots down her advances, and although it led to an altercation, they went back to being friends.
Justin tries a number of things to get Brian to love him back, including competing (and winning) the "King of Babylon" contest, stealing one of Brian's tricks, and dancing with guys Brian is interested in, and asking Brian to the prom, among other things. Despite initially turning Justin down, Brian shows up at Justin's prom and dances with him, kissing him in front of everybody. Justin described it as "the best night of [his] life." After his prom, he is bashed by a fellow student, Chris Hobbs, resulting in a two week-long coma, and brain damage that causes limited use of his hand. This event has impacted his life immensley and its effects are seen throughout the series.
Justin is accepted to Dartmouth College but opts to go to the Pittsburgh Institute of Fine Arts to pursue his dreams. With Justin's diminished use of his drawing hand, Brian gets a drawing computer for Justin to use. He continues his arts degree at PIFA and with Brian's friend Michael Novotny, creates a gay superhero comic called Rage, with stories often based on their own lives.
He experiences financial trouble when his father refuses to pay for his tuition. He resorts to becoming a go-go dancer at Babylon, despite Brian's repeated offers to help him out financially. Justin's new job takes its toll on him, the night shift causing him to lack energy during the daytime. After a disastrous experience at a party he was forced to accompany his boss to, where a number of men tried to rape him, he finally quits his job and accepts Brian's financial assistance. Justin starts a relationship with Ethan Gold, a fellow student and talented violinist, when he feels Brian isn't giving him the love and affection he wants. After Ethan cheats on him with a fan, Justin takes Daphne's advice and tries to win Brian back by getting a placement at Brian's advertisement agency. After a few tense weeks, Justin finally manages to seduce Brian once more in his office late one night. This sparks them to reconcile and continue their relationship.
On more than one occasion, Justin has saved Brian from legal problems. The first time, he blackmailed Kip into dropping the sexual harassment lawsuit against Vanguard and Brian. The second time, while he is still with Ethan, he makes Brian's nephew tell the truth about whether or not he had molested him. Justin drops out of college after a disagreement with the head of the internship program after it is discovered that he has been having sexual relations with his boss, Brian, and sabotaging Chief Jim Stockwell's ad campaign.
During the fifth and final season, Brian and Justin's relationship becomes more unstable. Justin works on a movie version of "Rage" but the project is canceled. When Justin returns from Los Angeles and moves back in with Brian, he expects them to settle down, which Brian still doesn't want. He leaves Brian, but after a bomb explosion at Babylon, Brian admits his love for Justin, asking him to marry him. They plan to get married, but as the date draws closer, Justin realizes that Brian is trying to become someone he isn't, just to make Justin happy. Similarly, Brian realizes that Justin is giving up his career as an artist to settle down with him. Brian tells him that he should go to New York City to pursue his art career. They agree to call off the wedding, saying "we don't need rings to prove we love each other."
Before leaving, Brian and Justin spend one final night together. Brian tells Justin that he's kept the rings, and Justin reassures Brian that they will continue to see each other frequently.
In November 2007, Justin was voted 3rd in the 'The Top 25 Gay Characters on Television' by AfterEllen's sister site, AfterElton. He lost to boyfriend, Brian Kinney and Jack McFarland from Will & Grace who came in 1st and 2nd places respectively.