Molly Lansing was born in the Glencoe tunnel following a horrific train wreck. Alexis Davis and Ric Lansing named their daughter Molly after the Titanic survivor, the Unsinkable Molly Brown. Before Molly was born, Ric and Alexis had contemplated divorce, but the birth of their daughter convinced them to try to make a go of their marriage.

In 2006, Alexis discovered the identity of the daughter she had given up for adoption, and Molly met her new big sister, Sam. After Alexis spied Ric and Sam making love, Alexis and Ric split, and Molly became a child of divorce.

When Alexis revealed that she'd been diagnosed with lung cancer and Ric knew she was smoking marijuana to ease the pain, he used it as a ploy to prove Alexis was an unfit mother. Ric sued for custody of Molly and won. When Ric's father, Trevor Lansing, threatened to take Molly away from him, Ric relented and let Molly live with her mother. Eventually Ric and Alexis agreed to joint custody. In 2009, Ric moved to Los Angeles and left Molly in Port Charles with Alexis.

Molly was an excellent student and an incurable romantic, so romance novels were high on her list. Because Molly's sister Sam's boyfriend, Jason Morgan, was decidedly unromantic, Molly took great pleasure in planning special romantic dinners and dates for them. Along with her sisters, Kristina and Sam, Molly schemed to get Alexis and Police Commissioner Mac Scorpio together. Mac was a surprise guest for Thanksgiving dinner and Christmas. Molly was thrilled when she saw Alexis and Mac kissing under the mistletoe. Alexis was onto Molly's scheme, but she genuinely liked Mac so she wasn't angry.

A precocious pre-teen, Molly was also known for her excellent pitching arm. At the General Hospital carnival, she succeeded in successfully dunking every guy in the "Dunk-a-Hunk" contest into the water tank.

Molly was very upset when Alexis' affair with Mayor Floyd was exposed, especially when she heard gossip about her mother at school and discovered unflattering postings about Alexis online. When Alexis found out, she prohibited Molly from using the computer.

When Claudia Corinthos was run off the road, Molly's cousin, Michael, was a suspect. When Michael fled Port Charles to avoid prosecution, Kristina went with him, leaving Molly to hold the fort at home. Molly was relieved when Sam tracked them down and took them home. Molly overheard Alexis confiding in her friend, attorney Diane Miller, that it was Kristina who had been behind the wheel and, in order to protect Kristina, Alexis intended to confess to the hit-and-run.

After Alexis was accused of murdering Mayor Floyd's mistress, Molly went to her cousin Nikolas Cassadine for help. Nikolas was able to reduce Alexis' sentence to community service. Alexis was upset that Molly had taken it upon herself to go to Nikolas, but Nikolas was impressed with his young cousin's maturity and told Alexis that she should be too. Ultimately, proof was found that it was the mayor's wife who had killed his mistress and set Alexis up to take the fall.

Molly and her cousin Morgan were the same age and were very close. Molly enlisted Morgan's help collecting water samples for a science project. They were down on the docks when they heard someone yelling for help. They traced the cries to a warehouse, where Johnny Zacchara was being held hostage by some thugs. Molly distracted the guards while Morgan freed Johnny. Johnny was very grateful.

Alexis and Molly liked Kristina's boyfriend, Kiefer. Under his perfect façade, Kiefer was abusive. One night, Alexis arrived at home to find Kristina badly beaten and barely conscious. Alexis grabbed her daughter and raced to the hospital, unaware that she had hit Kiefer, who was running from the house. Sam and Molly found Kiefer badly injured on the side of the road. He died from his injuries. When Kiefer's father, Warren Bauer, vowed revenge on Alexis and Kristina, a frightened Molly went to Jason and asked him to "make Mr. Bauer disappear." Jason explained to Molly that he couldn't.

When it was revealed that Dominic Pirelli was really Dante Falconeri, the son of Molly's Uncle Sonny, Molly met her new cousin. Dante was a cop and took no pleasure in being Sonny's son, but he embraced being a brother to Michael and Kristina and a cousin to Molly. Michael had confessed to Kristina, Morgan, and Molly that it was he, not Sonny, who had killed Claudia. The siblings kept his secret, but Dante found out and told the judge. Dante thought Michael would get community service because the killing had been in self-defense. The family was shocked when the judge sentenced Michael to five years in Pentonville. Molly was upset at the betrayal, but forgave Dante after he arranged for Michael's release. Molly couldn't understand why her Uncle Sonny was dating Claire Walsh, the prosecutor who had done her best to nail Sonny for the crime.

Molly was on a school ski trip when their bus crashed, leaving many students, including Kristina and Morgan, injured. Molly volunteered to help Michael flag down cars for much-needed help. After the accident, Molly began acting strangely. She threw a fit when Kristina wouldn't let her use her computer and smashed one of Alexis' vases. She said she wasn't feeling well so she could avoid receiving a reward for her bravery.

Molly thought she was bipolar and began an extensive search on the Internet about the disorder. She also had a heart-to-heart chat with her Uncle Sonny, who was bipolar, about the symptoms. One day, Molly heard a car crash, and she had a panic attack. Shawn Butler, an ex-Marine, saw her shaking and talked her down. Because he had suffered from posttraumatic stress disorder, Shawn recognized the symptoms. He was right, and Molly sought help in therapy.

Molly was beyond excited to be a bridesmaid at the glamorous Brenda Barrett's wedding to her Uncle Sonny. Alexis was running late for the ceremony, and Molly volunteered to look for Alexis at her law office. When she heard Theo Hoffman enter the office, she hid under the desk and overheard a conversation that revealed that Theo was the dreaded Balkan who had been targeting Brenda. Jason and Sam found Molly and swore her to secrecy. They promised to stop Theo before he harmed Brenda. When the limo with Brenda inside it blew up and Brenda was presumed dead, Molly suffered pangs of guilt for keeping the secret. Because Brenda had died for love, Molly swore she'd never read another romance novel.

The Balkan had engineered a switch and it was Sam, not Brenda, in the limo. When Sam suffered a temporary hearing loss, it was Molly who taught Alexis, Kristina, and Jason sign language. To Molly's relief, Sam recovered from the trauma.

Molly was "the family organizer." She sent a text message to Kristina, Michael, Morgan, and Dante to gather at Kelly's for a secret mission. Only family members were allowed. Molly's mission was to plan a surprise birthday party for her Uncle Sonny. Her plan went off without a hitch. Sonny was very surprised and very pleased.

However, none of the adults in Molly's life were pleased with the plans she made after the birthday party. She helped Kristina sneak away to join Ethan Lovett on his trip to the Dominican Republic to obtain a divorce and she plotted with Morgan to hide his sister Josslyn during a custody battle. After her nefarious escapades, Molly turned her focus to her family. Her sister Sam was engaged and Molly assisted in the wedding planning.

Around the same time, Kristina was hospitalized and required a surgery to remove a bone fragment near her spinal cord. Molly was concerned for her sister and Shawn provided Molly with advice in dealing with her concerns especially after she theorized that Kristina had sustained the injury months earlier when Sonny had planted a car bomb in Johnny Zacchara's car. Kristina had been with Johnny at the time of the explosion. Both Molly and Kristina struggled to comprehend Sonny's war with Johnny. Kristina made a full recovery and she and Molly were present to celebrate the marriage of Sam and Jason.

After the wedding, Kristina learned she had been accepted to Yale and left for college. Soon after, Molly had the opportunity to repay Shawn for the kindness he had shown her over the past months when a teenager named TJ moved in with Shawn. TJ enrolled in the same school as Molly and she offered to tutor him until he was up to speed in his classes. In return for her help, TJ offered to help Molly increase her popularity and he created an online persona on her behalf named Desdemona on a social networking site.

While posting as Desdemona, TJ invited dozens of teens to an underage drinking party at Molly's home on a night when Alexis was out. During the party, Molly unknowingly consumed alcohol and passed out. The party was broken up and Alexis assumed TJ had been behind the party. Molly tried to cover for him and claimed the party was solely her idea but TJ confessed instead.