Dexter arrives in Albert Square after finding a photograph and address for his mother, Ava’s family that she has recently been reunited with after being given up for adoption as a baby. Dexter meets his cousin, Abi Branning, and they quickly become friends, with Dexter being invited to a family dinner, though Abi and the rest of the family are unaware that Dexter is related to them until Ava arrives to take him home.Abi is angry with Dexter for lying and Ava is unhappy that Dexter has gone back to Walford. Later, Ava's car breaks down in Walford on her way to a job interview, so Dexter takes it to the local garage where he becomes friends with Abi's boyfriend, Jay Brown, and Phil Mitchell offers him work so he can pay for the repairs. Dexter becomes friends with Lola Pearce and is shocked to discover that she is a mother. Lola is disappointed by his reaction but they remain friends. However, Phil, who has custody of Lola's baby, Lexi Pearce, is unhappy about Lola and Dexter being friends and tells Lola to stop seeing him. When Bianca Butcher tells Ava that her son Liam Butcher is in a gang, Ava reveals that Dexter used to be in a gang, which turns out to be the same gang. Ava and Dexter give Bianca advice, but after the gang are arrested and released on bail, they trash Ava and Dexter's home. Dexter tells Ava they have to move away.
Ava decides to move to Walford and rents a flat on the Square. Dexter's father, Sam James, arrives unexpectedly and initially hides his true identity from Dexter, who takes a liking to him. When Dexter discovers the truth, he is angry at both Ava and Sam. Sam stays in Walford despite Ava and Dexter telling him to leave. Ava slowly realises she still has romantic feelings for Sam and they reunite. Dexter is initially hostile to this, but he slowly warms to his father. It emerges that Sam requires a kidney transplant. Dexter decides to take a test to see if he is a match, but Ava refuses to let him. He does so anyway, and he is a match, and Dexter and Sam go through the transplant operation. Ava fusses over both of them while they are recovering, and while Dexter is used to Ava's overprotective nature, Sam feels smothered. On Dexter's birthday, Ava discovers Sam came back to Walford to get Dexter's kidney, and ends their relationship, throwing him out onto the street. However, she does not tell Dexter the truth about Sam's departure, and he is angry with her, blaming her for his sudden disappearance. He moves in with Cora at the Branning's, and begins drinking heavily. He tries to kiss Lola but she rejects his advances as she is now with Peter Beale. He is fired from his job at the Arches after arguing with Phil and accidentally injuring Jay, and later, in a row with him and Abi, he reveals Jay's infidelity with Kitty to his stunned cousin. However, they reconcile and forgive Dexter for his wayward actions. After learning the truth, Dexter reunites with Ava, but when she goes to Newcastle for a new job, Dexter and Cora move in with Cora's boyfriend, Patrick Trueman, as they are no longer wanted at the Branning's.
In January 2014, Dexter clashes with Nancy Carter, when she refuses to serve him alcohol, and she later punches him in the face, after untruthfully exclaiming that he touched her bum. In March 2014, Cora and Patrick's relationship ends, due to her making some insensitive comments to their friend and neighbour, Dot Branning, about her deceased son, Nick Cotton (John Altman). After forming a close friendship with Nancy, Dexter realises that he loves her, although he is unsure whether she feels the same way about him. In May 2014, Dexter decides to tell Nancy how he feels, but she punches him in the face again, after mistaking him for an intruder. He later kisses her, and she is unsure how to react. After Patrick kicks Cora and Dexter out of his house, Cora's new friend, Stan Carter, who is Nancy's grandfather, gives Cora money to buy her own flat. Dexter then later stays with Ava for a while, returning in September in time for Phil and Sharon's wedding. He later begins a relationship with Nancy but she is upset when he leaves to stay with Ava over Christmas. Dexter later realises that his relationship with Nancy is not working out but gives her some heartfelt advice before leaving for Newcastle to stay with Ava.
Several months later, Lola and Jay start a relationship and plan to move to Newcastle with Dexter. However, Jay is arrested and sentenced to a three-month curfew, so Lola leaves Walford alone. Lola later calls Jay to end the relationship as she is now dating Dexter instead. In 2019, When Lola returns to Albert Square, she mentions to Jay that she and Dexter have since split up.