Josslyn John Jacks, daughter of Jasper "Jax" Jacks and Carly Corinthos-Jacks, entered the world prematurely while her mother was held captive by Claudia Zacchara. Claudia had intended to kidnap Josslyn to make up for the baby that she had miscarried, but her plans were thwarted by Josslyn's half-brother Michael. He killed Claudia and saved his baby sister and his mother from Claudia's diabolical plot. Not long after Josslyn's birth, the relationship between her parents deteriorated and Josslyn became gravely ill. She was diagnosed with kidney cancer, and her parents were informed that she required a kidney transplant. Josslyn received a life-saving kidney transplant when Jake Webber was killed in a hit-and-run accident.

After a bitter custody battle, her mother was awarded sole custody. Her father disagreed with the court's decision because Jax worried about Carly's penchant for getting involved with mobster Sonny Corinthos, and the dangerous impact that would have on Josslyn's life. Jax kidnapped Josslyn, but she was soon returned to her mother, and Jax left town. Josslyn was briefly kidnapped again, this time by Ewen Keenan, under the orders of her uncle Jerry Jacks. Josslyn was injected with vaccine to protect her from a deadly pathogen, but it had caused her to experience an extremely high fever. Jerry would later release the pathogen into the Port Charles water supply then demand millions in exchange for the cure.

Over the years, Josslyn would visit her father and grandmother, Lady Jane, in Australia for extended periods. She was close to Lady Jane, and she grieved deeply when she passed away on April 2, 2017. Josslyn also enjoyed attending Lila's Kids in the summertime and horseback riding. For years, Josslyn had been obsessed with horror movies, and wearing a cornstalk costume every Halloween. She was good friends with Spencer Cassadine, and she had had a crush on Cameron Webber in elementary school. Josslyn got along with Emma Drake, but she had considered Emma a rival for Cameron's affections.

In July 2016, a woman named Nelle Hayes arrived in town claiming to have been the person who had donated a kidney to Josslyn years earlier. Nelle told a tragic tale of woe about how her desperate parents who had been taken advantage of and tricked into selling their young daughter's kidney on the black market. A DNA test later confirmed that Nelle had been Josslyn's kidney donor. Josslyn immediately bonded with the young stranger because of their special connection.

Unfortunately for Josslyn, Nelle was a wolf in sheep's clothing who had a score to settle with Josslyn's mother. Nelle was the younger daughter of Carly's adoptive father, Frank Benson, and she resented that Carly had never tried to help lift Frank and his daughter out of poverty.

When Josslyn's brother, Morgan Corinthos, was killed in a car explosion on October 16, 2016, Nelle took advantage of the family's grief. She drugged Sonny then made it appear that he had cheated on Carly with Nelle. Carly ended her marriage and packed up her daughter then moved back to Carly's mansion. Nelle's deception was revealed, but Josslyn remained loyal to Nelle, certain that her actions had been misunderstood. Josslyn's older brother, Michael, had also remained sympathetic to Nelle.

Tensions escalated when Michael became romantically involved with Nelle, but the intense relationship ended in disaster. Michael ended things with Nelle, but she announced that she was pregnant. Michael realized that he needed to bide his time to secure custody of his child, so he pretended to reconcile with Nelle for the sake of the baby. Josslyn looked forward to becoming an aunt, and she remained unaware of Michael's ulterior motives for working things out with Nelle.

In the summer of 2017, Josslyn was at odds with her mother because she thought that Carly deserved better than Sonny, but Carly loved her husband. When Carly and Sonny took a short trip to his island, Josslyn decided to host a party. She called her friend Trina, and Trina invited the new boy at school that Josslyn liked, Oscar Nero. Classmates showed up with alcohol, but Josslyn didn't care because she only had eyes for Oscar. The two talked, and they immediately hit it off.

Oscar liked that Josslyn enjoyed real things like horseback riding rather than taking selfies and tracking how many likes they received. Josslyn's bubble burst when Bobbie arrived home and quickly put an end to the underage drinking. Josslyn landed in hot water with her mother, but she and Oscar began to hang out. He took her to a local footbridge to stargaze, and they talked about things that were important to them.

Carly reluctantly accepted Josslyn's new boyfriend because Oscar was respectful, and he had impressed Sonny. However, Carly was eager to meet Oscar's mother. Oscar explained that Kim Nero was a single mother who worked long hours at the hospital as an OB/GYN. Eventually, Kim agreed to attend a Thanksgiving dinner, but things took an unexpected turn when Kim met Jason Morgan -- Andrew Cain's identical twin brother. Kim hadn't known that Drew had a twin, so she had initially mistaken Jason for Drew.

When Carly and Jason tried to question Kim about Drew, she claimed that she had only known him in passing. According to Kim, Drew had dated a friend of hers. Josslyn suspected that Drew might be Oscar's father, so she stole a cup with Drew's DNA then sent it in with a sample of Oscar's DNA for testing. Meanwhile, Kim had reconnected with Drew, and she confirmed Josslyn's suspicions that Drew was Oscar's father. Josslyn was happy for Oscar because she knew that he had longed to have a relationship with his father.

Josslyn helped Oscar get to know his father, who had been abducted shortly after Oscar's conception on New Year's Eve, and held captive by the Cassadines. Oscar and Josslyn grew closer, but Oscar didn't have a high opinion of Josslyn's close friend, Cameron Webber. Oscar sensed that Cameron had a crush on Josslyn. Oscar was right.

Meanwhile, things had deteriorated with Nelle. In May 2018, Nelle accused Carly of pushing Nelle down a flight of stairs during Nelle's baby shower at the Quartermaine mansion. Nelle had been weeks away from delivery, and Carly was charged with two counts of attempted murder. Josslyn was stunned that her mother's dislike for Nelle had driven her to try to kill Nelle and an innocent baby. Nelle continued to manipulate Josslyn in an effort to drive a wedge between mother and daughter.

Several weeks later, Nelle attempted to kill Michael by asking an ex-lover to tamper with Michael's car. Detective Chase and Michael had been in cahoots, and the car had been rigged with a recording device as Michael confronted Nelle. Josslyn was devastated when she learned that Nelle had confessed to murdering Nelle's previous fiancé and gaslighting Carly. After Nelle forced the car off the road then escaped, she gave birth to a baby boy in the woods. However, Nelle secretly switched babies with Brad Cooper's adopted newborn son who had died of Sudden Infant Death Syndrome then claimed that her child had been stillborn because of the accident. Nelle was arrested and sent to jail.

Josslyn was brokenhearted by the loss of her nephew, and left reeling from everything that her family had endured, she began to shoplift. Cameron followed suit, but he was caught with a pair of stolen earbuds. Josslyn felt bad for leading Cameron down the wrong path, and she confessed to her mother on August 16, 2018 when Carly found a pile of stolen clothes.

On September 4, Josslyn set up a special surprise in the park for Oscar to celebrate their anniversary. Cameron helped her, but he didn't think highly of Oscar when Oscar failed to show for the date. Josslyn began to blame herself for pushing Oscar away with her recent troubles, but Cameron refused to allow Josslyn to shoulder the blame for Oscar's choices. Cameron told Josslyn that she was an amazing person then kissed her. Josslyn pushed Cameron away then reminded him that she loved Oscar.

Later, Josslyn learned that Oscar hadn't showed because he had collapsed. Oscar blamed it on low blood sugar, but he'd been lied to. A few days later, Oscar overheard his parents discussing treatment for his inoperable malignant brain tumor. Feeling betrayed by his parents for keeping the secret, and hurt that his time was limited, Oscar decided to spare Josslyn the pain of having to watch him die. He ended their relationship, but he confided the truth to Cameron.

Cameron began to see Oscar in a different light, and the two became friends, but Cameron also remained loyal to Josslyn. Cameron hated that Josslyn had been hurt. Eventually, Josslyn learned the truth about Oscar's cancer, and she vowed to stay by Oscar's side. With Josslyn's support, Oscar made peace with his family then agreed to undergo experimental treatment.

In January 2019, Josslyn and Oscar decided to start checking things off of Oscar's bucket list. They wanted to explore the catacombs under the city, so Josslyn suggested that they access them from a mine shaft at the abandoned Black Duck Distillery. Their adventure ended when Oscar suffered a seizure and collapsed. The situation turned dire when Josslyn realized that they were trapped in the mine shaft. She tried to climb out, but she fell from the ladder and was briefly knocked out.

The teens were saved when Jason, Sam, Carly, and Drew tracked them down. In early February, Oscar received a reprieve when scans showed that his tumor had stopped growing. Josslyn, Oscar, Cameron, and Trina decided to plan a daytrip adventure to Niagara Falls. Josslyn funded the trip with money that she had inherited from Lady Jane, and that Jax had set up in a secret bank account for Josslyn.

The trip ended in disaster when Oscar suffered a terrible seizure. He was rushed to the hospital, and Josslyn called his parents. Drew and Kim raced to Niagara Falls. Josslyn was startled when she ran into Jason in the hospital and he revealed that her mother had been admitted. Josslyn went to her mother, who had been recovering from an encounter with infamous serial killer, Ryan Chamberlain. Josslyn was in for another surprise when Carly revealed that Carly and Sonny were expecting a baby.

Josslyn was happy for her mother, and she confided that she and Oscar had planned to have sex for the first time, but Oscar had suffered a seizure. Josslyn worried that the news would not be good. On April 4, Oscar and Josslyn went to their footbridge, and Oscar gave her a padlock like the ones that lovers put on a bridge in Paris. Josslyn was touched by the gesture, and she marked the padlock with their initials. They found a spot on the bridge then clicked the padlock shut. Moments later, Oscar collapsed. He was rushed to the hospital, but he briefly slipped into a coma. Josslyn leaned on her mother as they waited for the test results.

The tests indicated that Oscar's tumor had grown, and he only had weeks left to live. Josslyn was brokenhearted, but she was determined to remain strong for Oscar as he and Kim moved into the Quartermaine mansion to spend the final days of his life surrounded by family. Josslyn and Oscar remained inseparable, and they worked on a special song that they hoped to perform at the upcoming Nurses Ball.