In 2002, Marcie Walsh was a student at Llanview University and volunteer at the local hospital. A good natured girl without a whole lot of friends, Marcie allowed herself to be talked into changing sonogram results for her new friend Jen Rappaport. At about the same time, Marcie began an unlikely friendship with Al Holden, a college student who was taking drugs in order to keep up with his studies. With Marcie's help, Al was able to kick his drug habit and the pair fell in love. Tragically, just as their relationship with blossoming, Marcie was attacked after participating in a peace protest and dumped in a dumpster. Although Al rescued her, he caught a disease and became deathly ill. Although, his mother was able to donate part of her liver, Al's liver was way too damaged from his previous drug use and he died.

Al's love for Marcie was so strong that not even death could stop him. Appearing to Marcie in visions, Al saw his chance to be with her in Marcie's new acquaintance, Michael McBain, a hardened, bitter young doctor who had lost his soul. When Michael died with Marcie present, Al's soul entered Michael's body. However, there was a catch--Marcie believed him to be Michael. That same day, Al's deceased stepmother, Luna, told Al that he only had until Valentine's Day to make Marcie recognize him. As the months went on, Al got closer to his goal, but then learned that he would lose his memories if he succeeded in getting Marcie to fall in love with Michael. On Valentine's Day, Marcie finally realized the truth when she saw Al in Michael's eyes. Al then told Marcie that although his spirit had to go to heaven, Michael would have his soul. With Al gone, Michael found himself in full control of his body, although his memories of courting Marcie were intact.

With Michael's support, Marcie began writing a novel, The Killing Club, based on a series of murders in a high school. When Michael, who was investigating Dr. Long on suspicion of wrong-doing, broke his leg to cover his tracks, Marcie decided to take over for him, and learned Long was selling organs on the black market. Long soon figured out what she and Michael were doing, and confronted the duo on a rooftop. Marcie nearly went over, but Michael saved her and Long was arrested. Unfortunately, Marcie had spent so much time on her book and the investigation into Dr. Long that she had neglected her studies, and she nearly lost her scholarship but Viki chose her and several other students to rebuild the community center. During her time in the Love House, Marcie took an active role in defending Mark Solomon, a fellow resident who admitted his homosexuality. It turned out that Marcie's brother, Eric, was gay, and she had spent much of her life defending him, especially from their less-than-understanding father.

Marcie and Michael began moving apart for each other as Michael spent more time on his medical career and Marcie concentrated on her novel. Her agent, Hayes Barber, pushed her to 'change her image' -- in particular, to lose weight. At Hayes insistence, Marcie was even considering liposuction, despite Michael's efforts to talk her out of it. Michael and Marcie broke up, but the two couldn't stop caring about each other. When Marcie saw Michael in an embrace with a nurse from the hospital (she kissed him), she ran out into the street, and was hit by an insane Margaret Cochran, who had Blair locked in the trunk. With Michael's help she was able to recover enough to get to the publishing party for her book, but the two still did not get back together. When Hudson Prescott and Julie Tanaka were found murdered, similar to the murders in her book, Marcie was horrified to think that she may be responsible, and donated the proceeds from her book to a fund in their names. Marcie, her father Charlie and her brother Ron, were attacked after Marcie's gas piping was intentionally loosened by the killer. They all survived, and the near-death experience pushed Charlie into finally accepting his gay son Eric and welcoming Eric's partner James into the family.

Overcoming difficulties from Michael's demanding hospital job and Marcie's newfound fame as an author, Marcie and Michael cement their relationship and marry on May 5, 2006. Marcie's father Charlie walked her down the aisle. Later that year, Michael and Marcie adopted a little boy they named Tommy, after Michael's deceased father. Marcie's friend (and Tommy's godfather) Rex Balsom soon discovered, however, that Tommy was actually Todd Manning's son, who had been kidnapped by Dr. Spencer Truman and was presumed dead. Knowing how devoted the McBains were to Tommy and recognizing Todd's volatile behavior, Rex decided to keep the secret to himself. Soon Rex's girlfriend Adriana and later Michael himself become part of the conspiracy to keep Tommy with the McBains. Michael decided to protect Marcie by not telling her. Rex went as far as to fake a death certificate for Todd's missing child to get Todd to give up the search. But in the wake of Spencer's murder, hints to the whereabouts of Todd's son began to surface, prompting Todd to resume his search. Marcie found out she could not have any children of her own just as the truth about Tommy's parentage came out. Todd took the McBains to court to win custody of his son, and both sides malign each other in a bitter battle. On October 9, 2007, Todd was awarded custody. As he arrived at the McBain's home to pick up his son, Marcie escaped out a window with Tommy and left town.

Marcie first showed up on the doorstep of her brother Ron. He gave her money and she barely managed to escape before both Todd and FBI agent Lee Ramsey showed up at Ron's door. Ron arranged for Marcie to meet a friend of his in Decatur, Georgia, under the alias Penny Shaw. Marcie arrived at a Decatur gay bar called Faces, posed as a drag queen and performed on stage to elude Ramsey, who had tracked her down there. Marcie's brother-in-law John, who was accompanying Todd on the search to ensure nothing happened to Marcie, spotted Marcie and started a bar fight so she could escape. Following instructions from Faces performer Clarence, Marcie headed to New Orleans and was helped by Clarence's sister Celia and her husband Wendell. John and Todd (now joined by Todd's wife Blair and nemesis Marty Saybrooke) made their way to New Orleans as well. John's car broke down, and Marcie was nearly caught again when Wendell, who has a towing company, received the call. Wendell covered for Marcie, who soon left for Paris, Texas, to meet up with one of Celia's friends.

A disguised Marcie walked into the Bon Jour Café, not realizing that Todd's sister, Viki Lord Davidson, had been working there incognito to temporarily escape her life. Celia's friend having quit months earlier, Marcie befriended waitress Gigi Morasco, who believed Marcie was fleeing an abusive husband and agreed to help. Gigi soon discovered the truth, but promised not to turn Marcie in. Marcie unknowingly avoided Viki, but was soon found by Llanview con man David Vickers, who wanted to claim the $1 million reward set by Todd. After a conversation with his in-the-dark friend Viki, the normally-selfish David decided that the right thing to do was to keep Marcie's secret. Rex soon tracked Marcie down in Paris, where Gigi lied and said that she had already left town. Gigi sold Marcie's wedding ring to Rex, who then used it to propose to Adriana back in Llanview. When Michael McBain saw the ring, he recognized it as Marcie's, which led them to find Marcie in Paris, Texas. Viki by this point also had come face to face with Marcie, who held Viki hostage inside the diner as the cops closed in. Michael exchanged himself for Viki and talked Marcie into giving up. Todd's son was returned to him and Marcie was arrested. Marcie was sentenced to community service and attempted to resume a normal life with her husband.

When 16-year-old Starr Manning became pregnant, Starr decided to give up the baby for adoption and asked Marcie how she would feel about adopting the baby. Marcie initially resisted but slowly warmed to the idea. Michael, however, was adamant that they could not adopt Starr's baby because Todd would never allow it and would never let them live in peace. After Marcie found out she could never adopt a baby through normal channels because of her history, she decided her only option was to adopt Starr's baby. Michael said he could not go through with it, however, and moved out of their home. Marcie decided she would raise the baby on her own and hope that Michael would one day change his mind. Michael and Marcie remained close during this period of separation, and one time they even made love, although Michael later was overcome with emotion. Todd told Marcie, Blair and Starr that he was not going to fight Starr's decision to give the baby to Marcie. Marcie wanted to believe him, although Blair was rightfully skeptical. Todd planned to steal Starr's baby and raise her with Marty Saybrooke, who had been told that Starr was willingly giving Todd her baby. However, Todd had a change of heart at the last minute. Starr gave birth to a healthy baby girl, and Marcie said she was going to name the child Hope. But before they could receive the baby, Jessica Buchanan -- under the influence of her alter Bess -- switched out Starr's healthy child for the stillborn baby that Jessica's alter Tess had just delivered.

Marcie was devastated at the seeming loss of Hope. Starr's obstetrician, Dr. Leah Joplin, had an autopsy performed and the results showed that the baby had died of RH disease, which sometimes occurs when a baby's father and mother have different blood types. Marcie gave Starr a locket containing a lock of the baby's hair, and Starr began wearing the locket every day to keep the memory of her baby close to her. Marcie and Michael bonded over the baby's death and reunited. Marcie struggled to move on with her life, and found herself drawn to the baby Jessica had delivered on the night of Hope's birth - unaware that Jessica's baby was in fact Hope. Marcie visited Hope's grave often, and eventually began to move on with her life. In March 2009, Marcie happened to see blood tests from Cole Thornhart, after he had been in a car accident, which showed that he had the same blood type as Starr's - meaning the baby hadn't died from RH disease. Marcie told Michael, and later Starr. But they agreed not to exhume Hope's body, which would be the only way to determine how she actually died. Little did anyone realize that Natalie Buchanan and her fiancé, Jared Banks, had stumbled upon the truth on their own and realized that the baby Jessica was raising was in fact Starr and Cole's child.

Michael and Marcie agreed when Starr and Cole eventually decided to have Hope's body exhumed so an autopsy could be performed to establish the true cause of death. But the autopsy raised more questions, since it proved that the baby that was buried wasn't Starr and Cole's child. Michael and Marcie vowed to get to the bottom of it, and were stunned when John revealed the truth to them: the babies had been switched at birth, and the baby they were supposed to adopt was actually alive and healthy! After an agonizing wait in which Jessica's alter absconded with the baby, Jessica finally returned to Llanview and handed over the baby to her grandparents, Todd and Blair. Starr and Cole said a quick goodbye to the daughter they believed had died and then handed her over to Marcie and Michael. To their astonishment, Todd agreed not to fight over the baby and even gave them money to help them raise his grandchild. Michael and Marcie were overjoyed to finally be parents, but then Marcie overheard Langston and Markko discussing how Starr actually didn't want to sign over the baby but felt obligated to do so because she had made a promise to the McBains. After talking it over with Michael, Marcie returned the baby to Starr and said that she should raise her. When Marcie returned home, Michael announced that he had just gotten an excellent job offer from Seattle Grace Hospital and said he wanted them to move away so they get a fresh start. Marcie agreed, and after both said their goodbyes to friends and family, they prepared to depart. Marcie then stunned Michael with the news that she was pregnant, and he lifted her up in his arms in celebration.

A very pregnant Marcie returned to Llanview briefly in November 2009 to celebrate Hope's first birthday. She also stopped by the cemetery to visit Chloe's grave and had a touching exchange with Viki. When Marcie returned to Seattle, she and Michael were surprised to run into Matthew Buchanan, who had run away from a boarding school in London and came to the Seattle hospital to have a risky operation to restore the use of his legs. Marcie faked going into labor to buy some time until Bo and Nora could arrive, but Matthew ended up in surgery anyway. Then Marcie actually went into premature labor and, with Michael by her side, gave birth to a healthy baby boy. They named the baby Gabriel (the male form of Gabrielle), thus fulfilling a vision from many years earlier in which Marcie's first love Al Holden - whose soul had entered Michael's body when he died - learned that Marcie and Michael would have a child named after Al's mother, Gabrielle.

Marcie and Michael returned to Llanview again in 2011 to visit John, again very pregnant with another happily expected child. Marcie visited Rex, reassured Destiny about her own pregnancy, and tried to get John to admit his feelings to Natalie before she married Brody.