Scarlett is the daughter of millionaire Tom King and Carrie Nicholls. Carrie nursed Tom's wife Mary as she was dying of cancer and their relationship continued after Mary's death, resulting in Carrie getting pregnant. After Scarlett was born, Tom ended the relationship but offered financial support. Carrie refused but allowed Tom to pay the fees for a private school.
Following Tom's death on Christmas Day 2006, his will revealed that he had a secret daughter with Carrie, who had attended the reading, named Scarlett Mary. Jimmy immediately realised that she was their half-sister, shocking Jimmy and his brothers when they learnt Tom had left her 25% of Home Farm and 10% of King and Sons to be held in trust until her 18th birthday. Carrie confirmed Jimmy's suspicions and told them that she and Tom had had a relationship but Tom refused to acknowledge Scarlett or tell them about his new girlfriend, worried about how they would react. Each of Tom's sons reacted differently to the news, Jimmy wanted to get to know Scarlett while Matthew wanted to buy her out and Carl saw her existence as a betrayal of his mother's memory.
Carrie was outraged to learn that the King brothers had been charged with their father's murder and warned them to stay away from Scarlett. She asked them to buy her out as she was acting as Scarlett's trustee, delighting Matthew. He wanted the shares cheap and to make sure this happened, he cut off all payments to Carrie, including Scarlett's school fees. The school suspended Scarlett as a result so Carrie confronted Matthew, leaving Scarlett in the car. However, Scarlett saw Jimmy and recognised him as he had recently visited Carrie and she followed him. She heard raised voices and after hearing Carrie refer to her as their “flesh and blood”, burst into the room and demanded an explanation. Jimmy explained that she was their half-sister but had only just discovered her existence after their father's death. Shocked, Scarlett ran away and Jimmy went after her, finding her on the main road. He took her to visit Tom's grave and told her that their father was “a good man”. On returning to Pear Tree Cottage, Scarlett asked Carrie why she hadn't told her that she had four brothers and Carrie replied that they were due to stand trial for conspiracy to murder her father. Shocked, Scarlett left with Carrie. Jimmy reassured her it was not true and they became close, Scarlett was also keen to get to know Matthew and Carl, much to Carrie's dismay.
On one of Scarlett's first visits, she met Daz Eden. She soon fell in love with him but he saw her as a friend and started dating Penny Drury. Scarlett was heartbroken when she found out but continued to fawn for Daz, much to Victoria Sugden's amusement. When Daz found out that Penny and Victoria had made fun of Scarlett, he was angry but went looking for Scarlett and on finding her, made it clear he was flattered but was still dating Penny.
A few months later, Carrie and Scarlett were visited by Scarlett's aunt, Lexi. Scarlett loved and admired Lexi but Carrie was indifferent to her and was shocked to discover that Lexi spent a year in prison in Mexico for drug trafficking. Scarlett was more concerned. The situation was tense between Carrie and Lexi and during a heated argument, Lexi told Carrie she knew that Carrie was her birth mother. Carrie refused to confirm that she was Lexi's mother so she left. When Lexi returned, Scarlett found out that Lexi was her half-sister and only her aunt by adoption and was horrified to discover that her mother had kept another secret hidden from her. Scarlett had gone from being an only child to suddenly being the youngest of six siblings. Eventually, Scarlett forgave Carrie and recognized Lexi as her sister, and they lived together until Carrie moved to Canada in February 2008.
Scarlett still had feelings for Daz and was happy to hear that he and Penny had split up. Persuaded by Lexi and Scarlett, Carrie and Jimmy agreed Scarlett could have a small party with a few friends. Victoria, however, announced the party on the internet so a large number of people arrived at Home Farm. Scarlett got herself drunk and told Daz she loved him, dragging him on to the sofa and kissing him, until they were interrupted by Jimmy and Carrie. Jimmy was enraged and chased Daz down the driveway.
Lexi persuaded Jimmy to let Scarlett go out with Daz and gave him money. When Scarlett found out, she felt humiliated. Carrie's relationship with Jimmy didn't last and she decided to emigrate to Canada. Scarlett did not want to go and Daz wanted her to stay as well. He revealed his feelings for her and they started dating. Lexi tried to take over as Scarlett's trustee, jealous of her younger sister's trust fund and determined to get some of the money for herself, but Matthew was appointed her new trustee. Disappointed in her older sister when this was revealed, Scarlett insisted on moving into Home Farm with her brothers, no longer wanting to live with Lexi.
On Scarlett's return from visiting Carrie in Canada, she lost interest in her schoolwork, feeling her inheritance from her father would get her through life. When she failed her GCSEs, Jimmy insisted she do resits at college. At Daz's suggestion, Scarlett bribed Zak Dingle to take her shopping instead of to college. When Jimmy and Zak's granddaughter Debbie found out, Jimmy nearly cancelled his contract with Debbie's garage, and Debbie nearly fired Zak. Scarlett then saw the consequences of her behaviour, and pledged to become more attentive to her education.
Things went well for Scarlett and Daz until she discovered he was having trouble paying his rent. She offered to have a word with Carl, who was his landlord, but Daz refused her offer so she suggested she move in with her, telling him that she could get round Jimmy's objections. Daz did not want to live with her, asking Jake Doland to move in instead as he was homeless. Jake suggested making the place a mess and then Scarlett would not want to move in. Jake was proved right when Scarlett saw the messy state of the house.
In December 2008, Scarlett's life fell to pieces when her bank got a court order to wind up King and Sons, due to their debts. On Matthew and Anna De Souza's wedding day, Carl visited the solicitor who revealed that Anna's father, Donald De Souza, was responsible for their financial trouble. Donald had recently died, leaving an interest in his company to Anna, making Carl realise that Matthew, as her husband, would stand to gain from the company's failing. This led to Carl and Matthew fighting, and ended in Matthew's death when he tried to run Carl over in a van. Following this, Scarlett, Carl and Jimmy were questioned and spent the night at the police station. The following day, she and her family faced losing everything. They were evicted from Home Farm and moved into Mill Cottage, which was owned by Carl and not the company. Scarlett argued with Carl and was upset by Matthew's death and the family's money problems. Carl thought she only cared about her trust fund being reduced but she offered it to them. Jimmy refused to take it, however, telling Scarlett that Tom had left the fund to her and it wasn't enough to help them.
Whilst she and Lexi packed their personal possessions, Scarlett told Lexi that she wanted to join their mother in Canada, feeling depressed with life in the village. Lexi pointed out that with all the recent events, it was not a good time to make big decisions and suggested that she did not leave until after Christmas. In January, Scarlett agreed to give life in the village a second chance when Carl started a new company and she decided to help him.
Carl bought a truck and started Emmerdale Haulage and Scarlett began working as his personal assistant. After being accidentally shot, Jimmy received £10,000 compensation if he agreed not to press charges and began helping Carl and Scarlett with the new company and took over as Scarlett's trustee.
Lexi, worried about her relationship with Carl, proposed marriage. The wedding date was set for 31 March and Lexi asked Scarlett to be her bridesmaid. Scarlett was thrilled and accepted.
In April, Scarlett and Daz went to Dublin for the weekend but the trip was unsuccessful as Daz was worried about Victoria possibly expecting his baby following a one-night stand. When challenged, she revealed it was a false alarm but Scarlett was devastated to discover that Daz had cheated on her with his own foster sister. Jimmy, Carl and Lexi knew there was a problem but Scarlett refused to explain. Daz's half-brother Andy Sugden asked Scarlett not to tell anyone and she agreed for her own personal reasons and not for Andy's concerns.
In June, Scarlett discovered that Lexi was trying for a baby with Carl and by July, Lexi was pregnant. But the pregnancy was ectopic and Lexi discovered that, without IVF, she was unlikely to conceive again. Scarlett and Jimmy's girlfriend, Nicola De Souza, supported her and Scarlett offered to pay for her and Carl to go to a private clinic. Lexi agreed, unaware that Carl did not want any more children, but changed her mind when she and Carl agreed that being together was more important. Seeing Carl with his newborn niece Angelica, however, hurt Lexi so much that when Carl told her they would never have a family together, she left him and went to Canada. Scarlett joined her at their mother's and returned to Emmerdale in September to find Jimmy, Nicola, Angelica, Carl and his new girlfriend and ex-lover, Chas Dingle, living at Mill Cottage. Furious, she sided with Nicola and they rejected Chas until Carl insisted they either accept her or move out. They accepted Chas and made an effort to get on.
In December, Scarlett celebrated her 18th birthday. Realising that Nicola was planning to spend her inheritance for her, she said she was leaving it in her trust fund until she was 21. Nicola was furious but Scarlett told Jimmy that she had her inheritance but didn't want Nicola to know. Nicola softened a little when Scarlett said she would set some money aside for Angelica but was angered when Scarlett said it would be tied up in investments until Angelica's 16th birthday. Towards the end of the month Scarlett began dating Adam Barton.
In September 2010 Scarlett learns of Adam's sister Holly's drug problem after Holly steals her purse. Scarlett does her best to support Adam and helps the Bartons meet up with Holly in Hotten after she runs away from home.
In December 2010, after learning of Carl and Eve's affair she decides to moves out and asks Adam to live with her and intends to buy a house form them but is not so keen. On New Year's Eve she witnesses Adam kissing Mia Macey. After a brief argument, Scarlett slaps Mia.
On 3 January 2011, Adam visits Scarlett and she makes up with him and forgives him for kissing Mia but he tells her that he does not want to live with her and that their relationship is not working and ends their relationship. The following day Scarlett decides to go to Canada to visit her mother and tells Nicola and Jimmy that she is over Adam. As they are getting into Nicola's car to give Scarlett a lift to the airport, they see Adam and Mia together and Jimmy loses his temper and angrily squares up to Adam and is about to punch him but Scarlett and Nicola hold him back and they get into the car and drive Scarlett to the airport.
She is concerned when Jimmy goes missing and is relieved when Jimmy is found. He returns to the village, suffering from amnesia. Scarlett tries to help Jimmy get his memory back. When Jimmy's ex-fiancée, Kelly Windsor, returns to the village, Scarlett is pleased to see her and defends her when Jimmy asks about Kelly's aborting their child. Scarlett is disappointed when it is revealed that Kelly had attacked Jimmy in Peterborough and gave him the injuries that caused his memory loss and insists that he does not owe Kelly anything but he refuses to report her to the police.
In July, Carl asks Scarlett for money to fund Chas's son, Aaron Livesy's, defence barrister when he is accused of murder. When Aaron and Chas reject his offer, Carl spends the money on new vehicles for the business and expands the firm. Scarlett is angry about this and feels betrayed by Carl. Matters worsen when Jimmy looks at her paperwork and realises that her business is struggling and she has been using her own money to prop up her business. Scarlett reluctantly admits that her business is doing badly and is angered when Jimmy claims that Carl's actions were for the best. Scarlett considers her future and decides that there is nothing left for her in Emmerdale. Whilst having a drink with Adam in The Woolpack, he convinces her to live life to the full and the following day, she books flight tickets and tells her brothers that she is emigrating to Mexico. Jimmy attempts to convince her to stay but is unsuccessful and he wishes her well. Scarlett bids farewell to Chas, Eve and Eve's great-aunt Edna Birch and Carl apologizes for using her money. As she gets into Jimmy's car, Carl also wishes her well and tells her to be good. Jimmy then drives her out of the village and to the airport.
Scarlett returns to the village in October 2012, following Carl's murder. She arrives in the offices of the haulage firm and is shocked to discover Charity Sharma has bought into the business. Rodney Blackstock fills Scarlett in on what has occurred since she left. Robbie Lawson flirts with Scarlett in the cafe and she catches up with Adam. Scarlett later warns her niece, Anya, Carl's daughter, about what Charity is like when she intends to buy Carl's share of the business from his children, if they had inherited them. The night before Carl's funeral, Jimmy gets drunk and tells a shocked Scarlett that Carl killed their father. Scarlett is disappointed that Jimmy had not told her sooner but forgives him. Scarlett attends Carl's funeral and comforts Anya during the service. The next day she accompanies Anya to a party held by Dan Spencer at the cafe and witnesses Anya flirting with Dan's son, Sean. The following week, Thomas and Anya leave the village to return to their mother. Scarlett warns them to contact her if Charity gets in touch with them about Carl's shares of the business before driving them to the airport. Scarlett chooses to stay in the village to support Nicola against Charity, who is attempting to convince Jimmy to sell the business.
Scarlett supports Jimmy at the reading of Carl's will and he is touched to discover that Carl has left everything to him. Jimmy changes his mind about selling the business, infuriating Charity. Scarlett and Jimmy celebrate. The following day, Scarlett gets ready to return to Canada. Nicola thanks her for her efforts to help and Scarlett invites them to come and visit her in Canada and bring Angelica with them. Jimmy bids her farewell and she gets a taxi to the airport.
- Scarlett has a fear of horses.