We are first introducted to Duncan Kane in the Pilot episode of Veronica Mars when Veronica is eating lunch alone and telling the stories of her previous friends where we find that Duncan is the son of billionaire Jake Kane (who perfected streaming video), and the brother of Veronica's best friend, Lilly Kane, who was murdered the previous year. It is also revealed that she and Duncan had dated the previous year before Lilly's death, and he had been her first love. However, their romance was cut short and ended suddenly without so much of a word from Duncan, and Veronica still wasn't really aware why it occured in the first place.

As season one progressed, Veronica and Duncan eventually got on better terms and could even be considered friends. However, when Duncan begins dating one of Veronica's only "friends", Meg Manning, things become awkward once again between the two of them. Tensions soon arise when Veronica, investigating Lilly's murder, suspects Duncan after she learns of his medical condition which causes him to act out completely out of character and enraged. In response to her accusations, Duncan quickly leaves Neptune only to be found towards the end of the season by Veronica's father Keith, in Cuba.

When he returns to Neptune, Veronica is dating his best friend, Logan Echolls, which sends Duncan over the edge and causes him to have an episode outside a party thrown for Logan, with his girlfriend Meg there to witness the whole thing.

Not too long after the party, Veronica, who was snooping around trying to find answers regarding her rape the previous year, finds answers from some of her peers that point the finger at Duncan. Determined to find the truth, Veronica confronts Duncan at his house where he reveals that the two did sleep together the night of her "rape" but the two of them had both been served drinks laced with GHB and it was in no way rape. The two then break down, and Duncan goes on to reveal that he still loves Veronica and the reason he left her alone was because he believed that she was his sister, and he still slept with her.

By the end of season one, Lilly's killer was unmasked as Aaron Echolls, Logan's father, whom Lilly was having an affair with. Veronica's father also had a paternity test conducted which confirmed that Duncan and Veronica were in no way related.

When season two began, Duncan and Veronica ended up back together after he gave her a fortune cookie that read "True love stories never have endings". While on a field trip that they both attended, a bus full of students, including Meg, drove off a cliff and killed all of the students excluding Meg, who was comatose.

Shortly after, it is revealed that Meg, still in a coma, is carrying Duncan's child. Both he and Veronica plot to kidnap the baby and have Duncan flee to another country to save the child from Meg's parents, who were revealed to be abusive. Veronica and Duncan succeed, and Duncan flees with the baby midway season two.

Duncan's last appearance is in the very end of the season two finale, where it is shown that both he and the baby (which he named Lilly), were in Australia. He put out an order for the death of Aaron Echolls (who was found not guilty of Lilly's murder previously), which was conducted by Clarence Weidman, Kane Software's security cheif. That is the last of Duncan that was seen in the series. His whereabouts are currently unknown, but it is assumed that he remains in Australia with his child.