Damien appeared in ten episodes.
Damien makes his first appearance in The Last Days of Disco Stick while visiting New York with his father, a Belgian ambassador. While there, he's slated to go on a tour of the city with Chuck Bass but ends up going with Jenny Humphrey instead. He uses them time to complete a drug deal, and she learns he deals because he is able to smuggle drugs into any country due to being the son of an ambassador. He brings her on a delivery that night, but they are caught by Chuck, who orders Damien and his father to leave The Empire because of the drugs. He continues to hang out dealing with Jenny (The Debarted), until he runs into Serena van der Woodsen. She is trying to make Nate Archibald jealous and asks Damien to go the French ambassador state dinner with him as his date. He agrees, and he ditches Jenny to go with Serena. Meanwhile, the two had planned for her to wear drugs into the dinner to give them to Princess Violet. Damien instead gives the jacket to Serena to wear, but she doesn't want to take it off and wears the drugs around. However, she ends up hooking up with Nate in the coatroom, and Damien and Jenny is able to get the jacket to Violet after all (The Hurt Locket).
Soon after, they are caught one morning hanging out in Jenny's room by Lily van der Woodsen. She calls Rufus Humphrey and Damien and Jenny are able to convince them that they didn't do anything inappropriate. Lily and Rufus decide to let it go, and after overhearing a conversation where Damien refers to her as a friend only, she reveals the pills to them. He explains to them that the drugs are his fathers and he only has them to make sure his father doesn't accidentally kill himself in an overdose. As a result, Rufus flushes the bag of pills and orders Jenny to move back to Brooklyn with him. Angry, Jenny abandons him before they leave to catch up with Damien (The Lady Vanished). She ends up being grounded in Brooklyn, only being allowed to leave for school. However, she cuts school to hang out with Damien at his hotel. Damien tries multiple times to get her to have sex with him, but she stops him every time. They eventually make plans for her to sneak out when Rufus goes to sleep so they can hook up. That day, Serena finds out that Jenny is sneaking around with Damien and plots with Nate to end their relationship. She has lunch with Damien, hoping he will try to make a move on her, but he doesn't. Meanwhile, Jenny is caught by Rufus who banishes her to her room and plans to take her to school himself every day and have someone walk her to each of her classes. That night, he plans to attend a ceremony to talk to Lily and brings Jenny with him. At the event, Damien comes to retrieve Jenny and punches Nate on their way out. They head to The Empire, and are about to do it when Jenny admits she is a virgin and is worried about what losing her virginity will be like. Damien plays it off like it's no big deal, but she realizes it is one to her. He leaves, saying he knew she was just a kid (The Sixteen Year Old Virgin). When she gets home that night, she tells Serena that she and Damien did have sex.
In Easy J, Jenny sends a tip to Gossip Girl; who reveals that she didn't lose her virginity to Damien as she said, but did to Chuck.
Damien makes his next appearance in The Townie, when Blair Waldorf and Dan Humphrey are in Cornwall, Connecticut searching for Juliet Sharp. He explains to them that a few weeks prior, Juliet bought a lot of drugs from him but he didn't know what for. They explain that Serena was hospitalized on an overdose, and the three figure there has to be an unexplained connection between Serena and Juliet. They got to her mother's house, and learn Juliet's brother is Ben Donovan. Afterwards, they head back to Manhattan and bring Damien back with them.
In Damien Darko, Damien runs into a newly freed Ben, and begins to taunt him when he learns Ben knows he testified that he saw him with Serena at an inn. It's also revealed he has begun hanging out with Eric van der Woodsen. At the W Party that night, Ben and Serena see Eric buying drugs from Damien. However, the two play it off by acting like they're in a relationship. Soon after, Ben physically threatens Damien unless he stays away from the VDW's. Afterwards, Damien calls Eric to hang out, and he eventually reveals that Ben threatened him. Eric asks Dan to help them get rid of Ben, and he hesitantly agrees to. At the W Party that night, Damien asks Eric to punch him and Dan to call Ben's PO to get him arrested for assault. Their plan works, and Ben is arrested. After the fact, Damien tells Eric that they can't be friends anymore and he was only using him to get rid of Ben. Eric then tells Rufus and Dan about what really happened, and Ben is released from jail. The next day, Nate and Dan tell Damien's father about his drug dealing (Panic Roommate).
Damien's father learning about the drugs causes him to be watched constantly, which is bad for business. He begins to blackmail Eric with the information about her forgery (It-Girl Happened One Night). On Eric's birthday, he fakes being sick to help Damien with his drug deal. Serena finds out, and enlists Blair to help her do it. However, due to her lack of sleep, Blair has Dan pick up the wrong flowers. That night, Damien arrives at the VDW's to collect the $100,000 Eric owes him to make up for blowing the deal. Lily finds out, and writes him a check herself to get him away from their family. Outside, Damien is confronted by Ben, who threatens to have him killed if he doesn't give the check back. He does so, but then goes to Bass enemy Russell Thorpe to get his money by revealing the secret about Lily. This is Damien's last appearance in the series.
In the finale The Return of the Ring, Serena calls Damien on her way out of town to buy drugs but he sends someone else to deliver them to her.
In the premiere Gone Maybe Gone, Georgina Sparks texts Damien wanting to know if he's seen Serena since she went missing. He replies that he hadn't heard from her since summer began when she purchased the drugs.
"I have a puzzle that needs solving, and I know how you Humphrey's like games."
"Oh, the old "make him jealous by bringing the titled European boy."
-The Hurt Locket (3x13)
"It's 9:30, I have Latin." -Jenny
"It's a dead language, it's not going anywhere." -The Sixteen Year Old Virgin (3x15)
"What, have you come to recruit another virgin to be your drug mule?" -Eric
"I would say "why, are you available?" but I'm leaving." -The Townie (4x11)
"You say potato, judge says pedophile. *Upon seeing Eric* Well, it's been great catching up, Mr. D, but my friend just arrived. I'd introduce you but you may or may not have statutorily raped his sister. Might be a tad awkward." -Damien Darko (4x13)
"Seems you van der Woodsen's and Humphrey's have a lot to talk about. Think I'm gonna get a cocktail, maybe some mac 'n' cheese." -While You Weren't Sleeping (4x16)
- He was a straight A student when he attended Knightley.
- He was raised by only his father.
- He had a crush on Serena when she was still at boarding school with him.
- He attended Le Rosey in eighth grade.