In The Girl Next Door, it was confirmed that Duncan had broken up with Veronica before his sister died. Previously, some viewers had speculated that the breakup occurred after Lilly's death. The end of Like A Virgin included a statement by Abel Koontz that Veronica's father might actually be Jake Kane. After that, it was speculated that Duncan may have broken up with Veronica because he believed her to be his sister. This statement was confirmed during A Trip to the Dentist when he tells Veronica that his mother had told him that Veronica's real father is Jake Kane (a statement which is later discovered to be false). In this episode, we also find out that Duncan had slept with Veronica after each had unknowingly consumed a drink laced with GHB.
In Season 2, Veronica and Duncan start dating again after Duncan gives Veronica a fortune cookie that says "True Love Stories Never Have Endings." Their relationship leads to a rift between Logan and Duncan - Logan is not only upset because Duncan is dating Veronica, whom he still has feelings for, but because he wasn't there for him all summer when he had to deal with being accused of the murder of Felix. Duncan is upset with Logan mainly for being so mad about Veronica, but he also harbors resentment over the fact that his dad killed Lilly, even though he knows that Logan and Aaron hate each other. However, they end up reconciling and remain best friends. Duncan and Veronica date for the first half of the season, until his ex-girlfriend Meg Manning dies, as a result of a blood clot which she sustained after surviving the bus crash which occurs in Normal is the Watchword. Meg had been carrying Duncan's child, which is delivered shortly after her death. In Donut Run Duncan and Veronica come up with an elaborate plan for Duncan to kidnap the baby girl (whom he renames Lilly) and take her to Mexico instead of allowing Meg's abusive parents to have custody.
Sometime after fleeing Neptune, Duncan is seen again in Mollymook, Australia talking on the phone with Kane Software security chief Clarence Wiedman, moments after Wiedman has completed Duncan's ordered execution of Lilly's killer and Logan's abusive father Aaron Echolls. A painting of Duncan is seen in The Bitch Is Back, as an homage to the character.
In the first two seasons, most people see Duncan as the 'golden boy' of the school (in contrast to his 'bad boy' friend, Logan), but while he is indeed kind and has a sense of honor, he also has a tendency to ignore anything that upsets or displeases him. Instead of telling Veronica that she might be his half-sister, for example, he broke up with her for no reason and wouldn't even acknowledge her presence in the school corridors. When he stops taking the pills his mother leaves him every morning, which are supposed to be for depression, he begins to have visions of Lilly much like Veronica. Lilly tells him that he knows there is more to her murder than meets the eye, that he should open his eyes and wake up. Unlike Veronica, Duncan is too disturbed by the visions to follow through and starts taking the depression medication again instead.
It is also implied that Duncan is attracted to Meg because she is like Veronica used to be. Although he quickly makes his move once Veronica and Logan break up, it is implied in a dream sequence that he is threatened by the hard edge Veronica has acquired. In the dream, Meg sits on a chair in a simple white dress asking him if he ever loved her, if he remembers all the times they had together. Veronica appears, dressed in tight black trousers and a see-through top with her belly showing, totally opposite to Meg. She states that she has heard enough. When Meg asks what Veronica has that she doesn't, the dream Veronica puts a black gag over her mouth and states "Well, I'm conscious... and that's just for starters." She then turns to address the camera (Duncan) and asks him if this is what he really wants, something innocent and sweet. She then says he should grow up and get over it, before lashing out with a slap. The dream shows the dichotomy of Duncan's mind (casting Meg as the virgin and Veronica as the whore) and the turmoil he is in over the two girls.
In Welcome Wagon, Veronica calls Duncan an "old friend" and gives Piz his clothes due to the theft of all his belongings.
A painting of Duncan is seen in The Bitch Is Back, as an homage to his character.
- "Oh dear God, may no one have just heard him say 'reign of Kane.'"
- "So now it comes out: Meg was one of those Britney Spears virgins, huh?"
- "I tried to just cut you out of my life. I loved you! I tried not to, I tried not to, but it won't go away!" (to Veronica)
- "You've been listening to Radiohead, haven't you? That's it. I'm putting you on a strict Nelly diet."
- "So, anyone read the paper today? Garfield. I mean, will he ever learn? Oh yeah, and there was this other thing...I guess Abel Koontz didn't kill Lilly."
- "Oh. Well, Mom was afraid that a ball would hit me in the face, Dad was afraid it would interfere with mock U.N., and I was afraid I couldn't hit a curveball." (on why Duncan never played baseball as a child)
- Veronica Mars
- Season One
- Credit Where Credit's Due
- Meet John Smith
- The Wrath of Con
- The Return of Kane
- The Girl Next Door
- Like A Virgin
- Drinking the Kool-Aid
- An Echolls Family Christmas
- Silence of the Lamb
- Clash of the Tritons
- Lord of the Bling
- Mars vs. Mars
- Betty and Veronica
- Kanes and Abel's
- Weapons of Class Destruction
- A Trip to the Dentist
- Leave It To Beaver
- Season Two
- Season One
- Veronica Mars: The Complete First Season, Warner Home Video, 2005, UPC 01256972774.