Born when his father was building up his empire, Jimmy didn’t have the same privileges as his brothers - and it often shows. He began working for his father at fifteen, after Tom bought his boss's failing factory. Charles Maguire was a thorn between Jimmy and Tom for some time, as an idealistic Jimmy disputed his father's tactics.
For many years, Jimmy was an awkward, dippy man, stumbling through business and a disastrous marriage. The closest enemy he had, apart from himself, was his brother Matthew, who coveted and eventually won Jimmy's place in the business and Sadie King's bed. As time passed, Jimmy and Matthew became closest in the family, and Jimmy found love with Kelly Windsor. Kelly, along with the arrival of their half-sister, Scarlett, made him a more caring individual.
His and Sadie's marriage seemed perfect. She was a stunning blonde determined to see him succeed as she had chosen him over Matthew because he was the oldest and therefore more likely to inherit the family firm. Sadly, they disagreed on one issue - he was desperate to be a dad but Sadie had no intention of getting pregnant. When Jimmy found out about this, he was horrified. Worried about her marriage, Sadie changed her mind but her determination to get rid of Charity ended their marriage for good. Sick of being made a fool of by Sadie and his family, Jimmy fell into Charity's trap. Sadie had convinced Tom that Charity was cheating on him so she got revenge and cleared her name by sleeping with Jimmy and videotaped him telling her about Sadie's lies. She blackmailed Jimmy for £200,000 not to play the tape to Tom and Jimmy paid her but she played him the tape regardless. The results were catastrophic. Sadie dumped Jimmy and Tom disowned him so he joined forces with a rival businessman - but this didn’t last. Tom soon forgave him and welcomed him back into the fold.
Relations between Jimmy and Sadie descended into war, further inflamed by Jimmy hiding his assets so Sadie's settlement was reduced. Angry, she bought land that Tom needed to get back into King & Sons. Jimmy was horrified and made it clear that the divorce was still going ahead, moving on to village vixen Kelly Windsor. They enjoyed a brief romance but Sadie ruined it by finding proof of Kelly's career as a glamour model. She told Jimmy so he ditched her. He went on to try and pull Woolpack barmaid, Toni Daggert, who hoped to become his PA, but Paddy Kirk ruined that so he concentrated on the business. Jimmy wanted to make Tom proud after Matthew walked away, leaving Jimmy in charge of King & Sons. Matthew and Sadie, however, plotted to ruin Jimmy and their scheming cost him a deal with Don Clough. Furious, he threw himself into launching the Kings River development on time but Matthew and Sadie paid Cain Dingle to drive a bulldozer into the show home, causing substantial damage. Jimmy had the damage assessed properly but wanting to open the show home on time, he just had the damage patched up, planning to have it repaired properly later. Unfortunately the damage to the gas pipes went unnoticed and the house exploded on the day of the opening, killing 3 people and injuring quite a few others, including Jimmy. His injuries were serious enough for him to need to go to a convalescent home for a few weeks and when he returned, he'd come to his senses and found that Tom was now involved with Rosemary Sinclair. All three King brothers tried to tell Tom that Rosemary was a nasty piece of work but he wouldn't listen. Their wedding was planned for Christmas Day and Tom even signed Home Farm Estates over to Rosemary but the day ended in tragedy when Tom fell out of his bedroom window.
The King brothers were among the primary suspects in Tom's murder, and were suspicious of each other. The lack of certainty about who was responsible ensured Tom's killer was never found. Matthew and Jimmy were horrified when they learned Carl was the killer, and relations between them were strained. After the funeral, Jimmy and his brothers were shocked to find out Tom had had an affair with their mother's nurse, Carrie Nicholls, which resulted in a daughter, Scarlett. Matthew wanted to buy her out of the family firm and Carl ignored them. Family man Jimmy embraced his new sister, becoming a surrogate father in Tom's place.
Jimmy and Kelly reconciled just before Christmas. Originally, Kelly told her family she planned to bleed Jimmy dry in revenge for Dawn's death but this didn't go as intended as she fell in love with him. After initially dumping her when he discovered her original plan, Jimmy realised Kelly really did love him and took her back. She supported him after Tom died, even giving him an alibi when she thought he might have killed Tom. Jimmy and Kelly got engaged. While planning their wedding, Kelly discovered that she was pregnant. Initially she seemed happy to have the baby, asking her agent how her career would be affected by her taking a year off and her agent, realising the implication, told her that her career would be over if she took time out to have a baby so reluctantly she had an abortion, thinking she and Jimmy could have children later. Scarlett accompanied Kelly to the clinic and noticed her reluctance, suggesting that they leave now if Kelly was unsure, but she went ahead. Scarlett told Carrie about Kelly's abortion about Carrie found one of the clinic's leaflets in Scarlett's coat pocket. Carrie angrily confronted her, disgusted by her deceit. Kelly pleaded with her not to tell Jimmy and Carrie agreed, providing Kelly stayed away from Scarlett.
On 9 October 2007 - Jimmy and Kelly's wedding day - two revelations came out, leading Jimmy to jilt Kelly. In the church, Jimmy saw Eli Dingle looking at Kelly as she walked up the aisle so Jimmy went for him, despite Carl's warnings to ignore him. Eli admitted kissing Kelly but insisted it hadn't gone any further because she was so upset about her abortion. Despite Kelly's obvious regret, Jimmy couldn't forgive her. Donna and Paul did their best to reunite them but nothing worked. Eventually Kelly went to see Jimmy and heard him tell Carrie that he would never forgive her. Heartbroken, she left but left Jimmy a letter, telling him she would be staying at a local hotel if he wanted to discuss anything but Carrie destroyed it and Kelly left the area. After Carrie Nicholls pursued him while engaged to Kelly, Jimmy gave in and they had a brief affair. However, things went sour when Carrie told Jimmy she loved him and he couldn't say the same, leaving her feeling humiliated. She realised that Jimmy had slept with her on the rebound and emigrated to Canada with an old flame while Scarlett chose to stay with her brothers and boyfriend.
However, financial problems built up and in December 2008, King and Sons were declared bankrupt and they were evicted from Home Farm, thanks to Donald De Souza's determination to ruin the Kings. On Matthew and Anna's wedding day, Carl learnt exactly what Donald had been up to and that he had left Anna an interest in De Souza Enterprises, meaning Matthew would also benefit as her husband. Feeling that Matthew had stitched his brothers up, he ruined the wedding which led to a massive fight between Matthew and Carl, ending only in Matthew's death. Jimmy was devastated at losing his brother, his home and the business that their father had built up. Carl was too embittered and stunned to help so Jimmy turned to drink, even drinking so much that he was drunk at Matthew's funeral. When he learned that Tom's grave had been defaced, he verbally attacked the whole congregation before Scarlett dragged him out. That night, Jimmy saw Shadrach Dingle hadn't filled in Matthew's grave so, weeping, Jimmy tried to do it himself. The next morning, Carl found him passed out next to the grave. The next day, Katie told Jimmy (thinking he already knew) that Rodney and Jamie Hope had arranged a shoot on Home Farm. Jimmy and a guest named Richard, realised Rodney was sleeping with his wife and went after Rodney, finding him at the B&B. Richard had a gun, and as Richard and Jamie struggled, Richard accidentally shot Jimmy. Fortunately, only his pride was seriously injured but this snapped him out of his wallowing. He and Carl began working together to restart the business and got a large settlement from Richard in exchange for not going to the police.
In February 2009 Nicola and Jimmy drowned their sorrows in the Woolpack and they ended up in the back of one of the Emmerdale Haulage vans. They kissed and events progressed further. The next morning, they woke up naked and on their way to Hull. Nicola was horrified; Jimmy was amused. Nicola felt she was too good for Jimmy and rebuffed his attempts at a relationship. A few weeks later, she asked him to go with her to Home Farm, as she thought the new owners, the Wyldes, wanted a sexual relationship with her. Jimmy was uneasy about returning to Home Farm and got drunk. When the Wyldes realised what Nicola had thought, they laughed at her and she spent another night with Jimmy. Nicola dumped him again, but when her father suggested that Jimmy might have some money hidden away in Switzerland (where he was going on a business trip), Nicola was suddenly interested. Carl told Jimmy that Nicola only cared about his money but Jimmy ignored him until Nicola proved Carl right. Jimmy humiliated her by wining and dining her, then when she arrived at the Woolpack with her luggage, she found a haulage van waiting for them. Jimmy told everyone she was a gold digger and left her at the roadside.
Sandy Thomas and Douglas Potts, who were living at the vicarage with Nicola, grew so tired of her presence that they wrote love letters in Jimmy's name, asking her to move in with him. Nicola genuinely did care for Jimmy, and jumped at the chance of living with him. Jimmy was shocked to hear about letters he'd never written but his happiness at being with Nicola made him stay quiet. Unfortunately Sandy wrote a similar letter to Betty and she read it out in the Woolpack and Nicola overheard. Jimmy admitted that he hadn't written the letter as he wasn't very good at that kind of thing and Nicola insisted he write her a love letter anyway. He tried but was proved right and after another argument caused by Jimmy telling Nicola she was curvaceous, which she interpreted as fat, he ended it and Lexi insisted that she move out of Mill Cottage, persuading Laurel to let Nicola move back into the vicarage.
In May 2009, Nicola discovered she was pregnant but decided not to tell Jimmy. Rodney told him instead and Jimmy wooed her into a reconciliation, planning to wait for her to tell him about the baby. When Nicola found out about this, she was furious and dumped him again and considered giving the baby up for adoption but Laurel made her realise she couldn't do it. Jimmy and Nicola bonded when they went for a scan and they decided to give things another go. Nicola returned to Mill Cottage and supported Lexi after her ectopic pregnancy and shock discovery that she was unlikely to conceive without IVF. She and Carl agreed to go for IVF as Scarlett was going to pay for them to go private but Carl told Jimmy (as Scarlett's trustee), not to release the money as he didn't want any more children. Horrified, Nicola told Carl to tell Lexi this or she would so he told Lexi and she threw him out, leaving Nicola to comfort her. Unfortunately this led to a fight and Nicola fell down the stairs. Lexi and Carl called an ambulance and Nicola and the baby got the all-clear but Nicola blamed Carl for the fight and told him so, warning him that he had to be honest with Lexi. On 6 August, Nicola gave birth prematurely to baby Angelica. She was in the special care baby unit for a few days but was fine. On 13th, Nicola went for a shower and Lexi took Angelica up to the hospital roof to show her the world. Although Jimmy, Nicola and Scarlett were terrified she'd harm Angelica but Lexi convinced Nicola to trust her and then Carl finally admitted to her that he didn't want any more children and never had. She returned Angelica to Nicola and after a verbal and physical fight with Carl, she left him and Emmerdale for good.
In July 2010, Nicola and Jimmy bought the Woolpack from Diane Sugden. However, in September, Jimmy and Nicola pulled out to spend more time with Angelica. Nicola noticed that Jimmy was becoming distant but didn't know why and he didn't know how to tell her that he was meeting Kelly in Peterborough and giving her money. Kelly suggests that they reconcile but still angry about the abortion, he refuses and they argue. Jimmy asked Kelly to leave the van but she wouldn't and fearing that he was going to hit her, she hit him with a torch and knocked him unconscious. She panicked and fled the scene, leaving Nicola and Carl to worry about Jimmy's sudden disappearance. The police found the van in Peterborough but Jimmy was nowhere to be seen. Jimmy is found days later in Nottingham and he is taken to hospital for treatment. However, when Nicola and Carl visit, Jimmy doesn't recognise them and it is clear that he has amnesia. Jimmy later returns to the village but doesn't remember anything or anyone, including his daughter. Kelly returns to apologise to Jimmy for attacking him and is shocked when he doesn't recognise her. Using this, Kelly convinces him that they were having an affair and that he was going to leave Nicola for her. Jimmy telephones Kelly and they arrange to meet in cafe but these plans were cancelled but Kelly returns to the village and introduces him to her son, Elliot. Jimmy is stunned to learn that he is Elliot's father and Kelly shows him and Carl DNA test results, proving her claims. Jimmy asks Kelly to keep this between them to avoid causing any more trouble but Rodney tells Nicola, leading to a fight between Kelly and Nicola in the Woolpack until Jimmy takes Kelly home. Jimmy is further manipulated by Kelly and she tries to get Jimmy's memories back by taking him to the spot where he had proposed to her four years earlier. Jimmy rebuffs Kelly's suggestion of reconciling, saying that he doesn't want to hurt Nicola and Angelica and offers Kelly financial support for Elliot's upbringing. Jimmy goes to church one day and remembers some of his and Kelly's wedding day, later telling Kelly that he remembered how much he felt for her at the time. Jimmy and Kelly sleep together, bringing back more memories but Jimmy feels guilty about hurting Nicola and Angelica but he tells Nicola about their relationship and asks for a divorce. Jimmy moves Kelly and Elliot into Mill Cottage soon after, much to Carl's discomfort.
Jimmy and Kelly have a play fight with a cushion. During this, Kelly hits him over the head and Jimmy remembers that Kelly was responsible for his injuries. He tells Nicola, who urges him to call the police but he refuses and later visits Kelly, demanding she tell him the truth. Kelly finally admits that she attacked him and caused his memory loss. Jimmy tries to win back Nicola but, is again manipulated by Kelly into spending time with her and Elliot instead of Nicola and Angelica. Jimmy later buys Elliot new clothes and Kelly hugs him. Nicola sees this and storms off so Jimmy offers to buy Kelly a house and support Elliot financially, reminding Kelly that he doesn't want her back, given her behaviour but Kelly refuses to take no for an answer. She deliberately goes to Mill Cottage with Elliot when Jimmy has Angelica and goads Nicola into attacking her when she arrives to collect Angelica as she is furious to see them together. Knowing that Nicola is on probation, she threatens to call the police as she thinks Jimmy will back her up but much to her horror, he warns Kelly that if she calls the police and reports Nicola, he will report her and take custody of Elliot. Not surprisingly, Kelly backs down and Jimmy suggests to Kelly that it would be for the best if she left the village. Kelly agreed and warned him that she will go as far from Emmerdale as she can, giving Jimmy an ultimatum that he either leaves Emmerdale with her and Elliot or never see his son again. Jimmy chooses to try and reconcile with Nicola and stay in the village and bids a tearful farewell to Elliot as Kelly drives out of the village. Jimmy resigns himself to never seeing Elliot again and desperately tries to make amends to Nicola but struggles to forgive him for sleeping with Kelly, telling him that she wants to go ahead with the divorce. In September 2011, they prepare to divorce but they later get into an argument and end passionately kissing each other. Jimmy and Nicola later reunite and Nicola and Angelica move back into Mill Cottage.
In late 2012, Charity worms her way into Emmerdale Haulage by getting an important contract that the Kings' needed, she gives them the contract on the condition that they give her 20% of the business, which both Jimmy and Carl reluctantly agree too. This led to Carl and Jimmy being unable to get on due to Charity driving a wedge between them, this resulted in Carl throwing Jimmy, Nicola and Angelica out of Mill Cottage. In October 2012, Carl is brutally murdered by rival Cameron Murray, leaving Jimmy the only King brother left. It is revealed in Carl's will that he left Mill Cottage, his shares in Emmerdale Haulage and his car to Jimmy, much to his surprise.
In January 2013, after it was revealed that Carl's son Thomas King had been the one who had been stalking Chas Dingle, Jimmy and Nicola took Thomas in and allowed him to stay with them permanently at Mill Cottage on the condition he stop his revenge campaign against Chas and either got a job or go back to college.
In late September 2013, Jimmy feel asleep at the wheel of a truck, which results in him crashing.
- Jimmy has a passion for the reality show Ice Road Truckers. He even had a poster of driver Lisa Kelly on his bedroom wall until Nicola made him take it down.
- Jimmy has a phobia of horses.
"Broken down?" (First line, to his brother Carl)
"It's never been easy for me, first born but always second best" (After Matthew gained control of the company instead of him)