They first met when Debbie got in a fight with Holly and her friends over Debbie allegedly raping Matt. She develops a crush on him and begins to take lessons boxing at his gym.
They become friends, but Debbie wants to be his girlfriend, not his friend. Eventually, she begins to tell him this when he kisses her and they begin their relationship.
At one point they were about to have sex, though Debbie’s sister Fiona walked in on them because Debbie had left her brother Liam unattended. This was awkward for the teens and Derek decided to go home since his father would get on his case.
In the finale, Debbie realizes she wants him to be around forever. Debbie intentionally stopped taking her pill and has sex with Derek. Debbie finds out they're having a baby and expected him to be around. However, Derek is overwhelmed with the news of being a teen father, that he goes to Florida to live with his grandmother. Derek’s family also accuses Debbie of trapping him.
He returns and tells Debbie to stay away from him, feeling (correctly) that she trapped him and didn't consider his position.
He is mentioned in episode 8 ("You sold me the laundromat, Remember?") Debbie goes to make amends with his sister-in-law Tanya, who called DCFS on her, and they talk about how he's been asking about Franny.
He visits his mother on her birthday, though he comes with his fiancée, Peppa. In the visit, Derek meets and bonds with his daughter who his mother was babysitting. When Debbie comes to pick her up, a tense meeting is made since Derek had left all the caring for the baby to her. Now guilty for his previous behavior, Derek tries to make amends by offering to cover his child's needs.
It's revealed in A Little Gallagher Goes A Long Way, that Derek had died in a dishonorable fashion; having gotten "Sideways drunk, stole the tank, drove it into the Suez Canal" and had thought said that the tank was a submarine. According to the army, Derek’s body is still buried beneath the sea in the tank which is worth nine million dollars. It was mentioned by the army, there are highly-dedicated jihadists who have done less damage than Derek did with his stunt. Debbie was horrified to learn this information out from Peppa and wishes for her to give her a portion of Derek's death benefits from the military only for Peppa to close the door in disgust.
- A Night to Remem- Wait, What?
- Rite of Passage
- Crazy Love
- Tell Me You F**king Need Me
- Uncle Carl
- South Side Rules
- Love Songs (In the Key of Gallagher)