|Portrayed by||Katie Jarvis|
|Introduced by||John Yorke|
|First Appearance||9 February 2018|
Hayley Slater made her first appearance on the 9th February 2018 and she is the cousin of Stacey Slater.
Hayley is first seen in Walford taking photos of Stacey and Martin Fowler. Whilst in the café, Hayley looks through her phone and answers a phone call, asking if the caller had received any photographs. She insults Martin to the caller, reassuring them that she knows what to do next.
Hayley introduces herself to Martin at his stall on Bridge Street and helps herself to an apple. Later in the café, Hayley distracts Martin when he is looking after his daughter, Hope Fowler and Stacey catches Hayley kissing Martin. In Martin's absence, Hayley whispers to Stacey her identity as it was unknown to Stacey that Hayley was in fact her cousin. Martin meets up with Hayley whilst he is looking after Hope and his adoptive son, Arthur while Stacey collects her seven-year-old daughter Lily up from school. Hayley encourages Martin to keep the children out for longer, disobeying Stacey's instructions. Hayley pretends to defend Martin in front of Stacey when she collects Arthur and Hope with police presence due to Martin not returning them at the time agreed.
Hayley arrives in Walford once more, asking Mo Harris for her share of money from the sale of the SIM cards. When Hayley demands her money, Kat forcibly orders her to leave Walford. It is then noted that Hayley is currently homeless and after spending the night sleeping rough, Stacey's mother Jean Slater invites Hayley indoors where she opens up to Jean about her upbringing and being excluded from the Slater Family. Hayley is barred from The Queen Victoria when Linda Carter finds Hayley slept in the same bed as her husband Mick Carter; it was then revealed Hayley only did this to try and split up Mick and Linda after being paid by Stuart Highway, who used Mick's money to pay her.
Whilst Martin is trying to reconcile with Stacey, he discovers that Hayley and Stacey are related and that he was 'set up'. It is later revealed that Hayley is pregnant, despite heavily drinking, but by binding her stomach she is hiding her pregnancy. Hayley befriends an 16 year old homeless girl on the tube, Brianna, who steals money from Hayley that she conned out of a man named Craig, by making him believe she was a prostitute. Brianna notices that Hayley has a baby bump and asks her how far on she is.
The next day, Jean finds Hayley and she tells her that she can move into Stacey's house alongside the rest of the family, like Jean, Stacey, Stacey's cousin Kat Slater, their Nan Mo, Stacey's kids Lily, Arthur and Hope and Lily's auntie Whitney Dean and her sister Tiffany Butcher. A while later in the Queen Vic, Hayley goes to the bathroom and raps a bandage round her stomach so no one will suspect that she is pregnant, however a woman warns her that it is dangerous for the baby, so Hayley stops.
On the night of the Royal Wedding, after Mo and Kat Slater give Hayley a makeover, Jean passes her an umbrella as Kat and Mo plan to tip water on her. Hayley then goes outside to confront them and they stop. She then heads to a hotel room outside of Walford where it is reveled that Kat's husband Alfie Moon is the father of her unborn child after they had a on night stand. The pair talk and Alfie asks about Kat because Kat's son Tommy (who is the biological son of Alfie's brother Michael Moon) and Kat and Alfie's twin boys Ernie and Bert need to see their mum as Aflie is currently raising them after a fall out with Kat - which has made Kat refuse to even see her boys. Alfie tells Hayley he loves Kat but Hayley tells Alfie she thinks the baby is a girl and she could boss her big brothers around and Hayley will raise them as her own. However Alfie replies by telling Hayley that Kat is the boys' mother, not her. Hayley gets mad and wants to have an abortion but Alfie tells her not to but later changes his mind after Hayley talks him round. Alfie gives her the money and the next day Hayley makes an appointment at the hospital for a termination. Hayley then gets drunk and turns up late to her appointment, which makes them refuse to see her. She then makes a new one but changes her mind after Kat tells her she's a good person really.
A few weeks later Hayley is shocked when Stacey announces that her and Martin are back together and he will be moving back into the house. The Slater's then get an even bigger surprise when an envelope is put through the letter box saying Slater's. They all don't know if to open it or not and Hayley tells everyone that she is the only Slater. While pointing to Tiffany, Stacey, Mo and Jean, she arrogantly says "Fowler, Harris, Walters - oh and Buchard" to prove a point that she should open the letter as she is the only Slater in the house. But Tiffany very sarcastically replies to Hayley saying "It's Butcher, actually".
Stacey open's the letter and to their surprise, it is the key's to Charlie Slater's old cab, with a note reading telling them that Charlies friend had the cab and he promised Charlie that when he retired he had to give the cab to the Slater's. Hayley tells Stacey she can fix it but she doesn't believe her so Hayley goes to see fellow mechanic Keanu Taylor where she asks if there is any jobs, however she didn't really want a job and was just trying to destract him while she stole some tools to fix her Uncle Charlie's cab. Later on she uses Tiffany's laptop so she can go online and see if anyone is interested in buying the cab. Tiffany spots her and this causes them to argue. Stacey pulls the pair apart but Tiffany goes to slap Hayley which causes another fight to break out. Stacey pulls them apart once again and while Tiffany's back is turned, Hayley eats her piece toast - which makes Tiffany mad.
On 22 December 2017, executive consultant John Yorke announced a new member of the Slater family would be introduced into EastEnders among the returning Slaters, to "sort Stacey out" after her big 2018 storyline. Hayley's connection to the Slater family was not immediately revealed upon the character's debut, but it was announced that she would be involved in "a brand new mystery" for Martin. Duncan Lindsey, writing for the Metro, suggested that Hayley could be connected to the Slater family, either helping Stacey fight against her estranged husband Martin or a new family member. The reporter also suggested that Hayley could be acquainted with Martin's former stalker, Sarah Cairns (Alison Pargeter). It was reported that Hayley would not be friends with Martin, who will have to "watch his back" throughout his custody battle with Stacey. The character was revealed as Stacey's cousin in her third episode. Of her casting, Jarvis said that she is "really excited to join a team of such lovely, talented people and become part of such an iconic show" and loves being a part of the Slater family, commenting that it is "going to be so much fun and I cannot wait to see what’s in store for Hayley.”