Sean arrives in Walford on 22 August 2006, to take revenge on the newly arrived Al, who is responsible for Sean losing his job in the Army. He breaks into Al's flat and follows him into the Queen Victoria pub where, by chance, he sees his sister Stacey, whom he had lost contact with for seven years. After taking revenge on Al, Sean decides to stay in Walford to look after his sister. Sean immediately begins pursuing Tanya Branning, before deciding to date Ruby Allen after learning she is wealthy. Sean soon proposes marriage but continues to pursue Tanya and has sex with numerous other women, including Karin Jones and Preeti Choraria. However, when Ruby Allen starts interfering in his relationship with his mother Jean Slater, Sean is so angry that he splits from her.
In 2007, Sean starts dating Chelsea Fox and also has sex with her stepsister Carly Wicks , causing a number of rows. Scorned, Chelsea and Deano Wicks try to get revenge on Sean by attempting to frame him for assaulting shopkeeper Patrick Trueman. Sean's attempt to escape arrest fails and he is held on remand. From prison, Sean has Deano attacked so Carly ends the relationship, but discovers that Chelsea has CCTV footage proving that Sean did not attack Patrick. Despite her family's protests, Carly takes the footage to the police. Sean is released, and Deano and Chelsea are arrested for conspiracy to pervert the course of justice. Sean takes revenge by cutting Chelsea's hair while she sleeps and assaulting Deano again.
Sean and Tanya Branning start dating at the beginning of 2008, and Sean tells her that he was responsible for his father's death. In March 2008, they plot to fake Tanya's reconciliation with Max Branning in order to gain control of his assets and then leave the country. Tanya pretends to split up with Sean and reunite with Max, but secretly they conspire to bury Max alive. However Tanya feels guilty and releases Max. Much to Sean's surprise, Tanya scorns and rejects him when he says he wants them to be a family and reveals that she used him to get revenge on Max. Sean threatens to tell her children what she has done but Tanya retaliates by threatening to tell Stacey that Sean killed their father. Sean keeps quiet but takes the rejection hard. He then begins dating Roxy Mitchell and torments his flatmate Gus Smith. Sean reveals that he plans to kill Gus and make it look like suicide but Stacey stops him and makes him move back in with the Slaters. Roxy and Sean split up, and Gus reveals to the Slaters that Sean is involved in drugs
When Roxy reveals that she is pregnant, Sean assumes that he is the father, unaware of her one night stand with Jack Branning. He offers to support her but Roxy refuses his offer and returns to Ibiza. Sean leaves Albert Square briefly and returns in July after learning that Roxy is in Weymouth with her father, Archie Mitchell, so he goes to see her. Archie encourages Roxy to stay in Weymouth with him but her sister Ronnie Mitchell and Sean persuade her to return to Walford, and she moves in with him. Ronnie disapproves of Roxy and Sean's relationship as she suspects him of selling drugs, but comes round after they get married in August. Sean has a difficult relationship with Roxy's father, Archie, and is unhappy about accepting his money for a deposit on a flat. On 13 November 2008 when Roxy goes into premature labour, Archie pretends to call Sean but doesn't so he misses the birth of Amy, On christmas day 2008 Sean opened a cracker and then BANG, Sean finds out he wasnt Amy's father angered by this also knowing Jack's the father he kidnaps Amy but Stacey Slater beings Amy back Sean and Roxy the sort things out Roxy rides of with Sean unknowing what he is planning (To kill them and himself) Jack and Ronnie later track them down Roxy manages to get out the car and runs onto the ice so Ronnie and Jack can get Amy the ice breaks and Roxy and Sean fall in the lake Ronnie jumps in to save Roxy, Sean later breaks out and he starts to walk towards Roxy but she tells him to go Sean then walks off slowly into the darkness, Sean has been mentioned a quite a number of times since the square.
The key 2015
On 1 May 2015, Stacey Slater makes a video call to her brother Sean via Skype, however, while he does not appear on screen, he reminds her to take care of her mystery key due to its link to their father. When Jean reacts badly upon seeing her with the key, Stacey attempts to find out what the key represents but Jean catches her and, unwilling to tell her the truth other than Sean apparently couldn't trust her with it, seemingly throws it down the toilet. However, after Stacey leaves, it is revealed that Jean still has the key. She returns the key to Stacey four months later, revealing that it unlocks a deposit box in which Brian left Stacey and Sean some information about his other family, but Sean took the key from Jean after Brian's death before she could give it to Stacey when she turned 21.
When Jean is diagnosis with cancer Shirley Carter Issues a Idea of a bucket list In which Jean thinks about and eventually comes up with the Idea of finding Sean, Shirley spots the writing Jean dotted down on a piece of paper stating "Find Sean" In which Shirley tells Stacey, Stacey layer rings Sean but Sean acts strange on the phone which worries her and eventually tells Kat that she has contacted Sean in which Kat wasn't happy about both Kat and Stacey decides Its best not to tell Jean that Sean has already been contacted and knows of her illness but Jean later finds out when Stacey snaps telling her Sean knows about her illness the same day Jack Branning texts Stacey to pick up his daughter Amy Mitchell from school when arriving at the school Stacey feels like Amy should of came out as shes taking longer then expected only for them to find out that she has already been picked up, We then see Amy In back of the car asking the question "Did my Mam really send you?" In which Sean turns around and replies "Yeah!, Yeah she did".
Sean takes Amy to a cafe to buy her a milkshake and Sean talks about Roxy unknown to him that she is dead and not realising Amy's pain, Sean later takes Amy home to where Jack finds her and beside himself with worry and is even more shocked when he sees Sean, Jack sends Amy away as Amy leaves Jack grabs Sean and threatens him then asks him what he wants In to which Jack is shocked and taken back when Sean says his come to see Roxy, Realising Sean doesn't know Jack grabs his car keys and tells Sean to follow.
Sean and Jack pullover to a church where Sean asks him where Is he taking him and also asks Jack if he is still with Ronnie Branning also not known she died with Roxy when Jack reveals to Sean they both Ronnie and Roxy are dead Sean is sad and shocked and asked Jack what happened in which Jack explains but then puts all the blame on Roxy In which Sean does not like and eventually punches Jack to the ground In which Jack responds and a fight erupts after a quick fight Sean and Jack have a heart-to-heart in which Jack offers Sean a lift back to the square but Sean wants to spend more time in taking In the news Roxy is dead.
The next day Sean wakes up In his car and looks In a the car mirror to which he looks upon a black eye from his fight with Jack the previous day, Later that day Sean walks in the Vic in which Jean is shocked and happy to see him while both Kat and Stacey are shocked to see him, Ruby Allen walks in and sees Sean and walks up to him and slaps him after the way he treat her twelve and a half years previous but Sean shrugs it off and takes Jean to her appointment in during which Stacey has a go at Sean, and Jean suggests going away for them to catch up in which Sean agrees.
Jean and Sean pack off to go away, Sean takes Jean to an abandoned farmhouse supposedly been living their since returning from Ibiza the two talk and tell each other what they have been up too the last yen years In which Its clear Sean wants to tell his mother that his responsible for his fathers Brian's death but Jean cuts her leg and later feels unwell Sean manages to call an Ambulance and Stacey but leaves Stacey worried by his call, Sean later locks the barn and smashes the gun cupboard and takes a shotgun after 'talking' to Roxy saying that Amy Is like her and Jack has done a good job In bringing her up he plays a voicemail from when he was with Roxy In 2008, Jean and Stacey later find Sean sitting their angry he reveals to Stacey that he killed their dad to Stacey's shock after a intense arguments Jean manages to talk to Sean and Sean eventually asks for forgiveness In which Jean does forgive him for killing Brian as too does Stacey.
Back at the Slater's house Jean, Kat and Stacey come up with a plan to help Sean but he wants to move on and reveals to Jean he's booked himself into a mental health facility. Before Sean drives off he sees Amy and shouts her over. Jack asks Amy what Sean wanted and Amy told Jack that when she's 18 he will take her to her mother's best bar In Ibiza.
Johnny Allen (October 2006: instigated/unintentional) – Sean taunted Johnny while visiting him in prison, enraging him to the point where he suffered a heart attack and later died in hospital.
"Adiós amigos!" (Final line to Jack Branning, Jean Slater and Amy Mitchell before leaving Albert Square in a car to seek help).