Michael McBain grew up in Atlantic City. When his father died, he was raised by his mother Eve and his older brother John. Michael left home to attend boarding school on a scholarship. College followed and then medical school. Along the way, Michael became soulless. He came to Llanview and started interning at Llanview Hospital.

When Al Holden died, his love for Marcie was so strong that his spirit came back to earth. Appearing to Marcie in visions, Al saw his chance to be with her when Michael died after taking the wrong medication. Seeing another chance, 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 to 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. After a final kiss, Al left for heaven, and Michael and Marcie had no recollection of his ever being there. However, both did remember their courtship of the last few months and started a new relationship.

Michael began a campaign against Dr. Long, the then Chief of Staff of Llanview Hospital. Dr. Long had scolded Dorian Lord for having Michael, a first year resident, care for Viki Lord Davidson, who was having heart problems. He later saw Dr. Long sneaking a peek at someone's medical chart.

During another incident, Dorian saved a little girl's life after she had a violent reaction from a bee sting, which impressed Michael. Dr. Long was angry because Dorian was an administrator, not a physician, at the time. Michael came to her defense, but Dr. Long berated him. Michael and Dorian then saw Dr. Long talking with Paul Cramer and found it rather curious, especially when Michael mentioned that he'd seen the man around the MedEvac flight choppers.

Michael began to investigate Dr. Long after learning that he donated a dead patient's organs, even though the widow insisted that no donor card had been signed. Determined to find out more about Dr. Long, Michael broke into his office while Marcie stood guard at the door. However, Michael broke his leg after falling out of the window trying to escape when Dr. Long returned unexpectedly to his office.

While Michael was hospitalized, he spied on Dr. Long and Paul, despite warnings from John and Marcie. Dorian found out about Michael's spying and said that she wanted to know what was going on as well.

Michael convinced his cousin Shannon to spy on Dr. Long, but all she got was pictures of Natalie and Paul kissing on the helipad. Dr. Long later snooped around in Michael's hospital room, but Michael pretended to be asleep. Michael suspected Dr. Long of stealing donor organs, these suspicions were confirmed when Dorian informed him and Marcie that a donor heart was stolen.

Later, Dr. Long tricked Michael by mentioning a trip to Atlanta. Michael and Marcie then attempted to break into Dr. Long's office, only to get caught. Michael threatened to tell the police about the doctor's harvesting organs and auctioning them off, as well as suspicious helicopter flights and removal of organs without consent. When Dr. Long presented them with what seemed to be authentic signed forms and documentation, Michael and Marcie became apologetic. Dr. Long was supposedly the Northeastern Director of Transplant Coordination. Dr. Long then called the police to arrest Michael for breaking and entering. After a cop arrived, Dr. Long told him that it was a misunderstanding, giving Michael and Marcie a second chance. Once they left the office, Michael pulled out the file, which he believed to be fake and planned to turn it over to the police.

Marcie brought Michael home from the hospital. Michael was convinced that the papers Dr. Long had shown them were fake and that he was selling the organs illegally. They decided they needed to find someone to pretend to be the relative of a rich person that needed a transplant and that way they could get the proof they needed against Dr. Long. John showed up to yell at them, he had learned from the police that Dr. Long had almost had Michael and Marcie arrested. He promised to look into it and find out what Dr. Long was up to.

Michael and Marcie began to receive threatening phone calls. Michael began to have nightmares, and a window was broken at Jen's house, where he and Marcie were staying.

Marcie then went to the hospital while Dr. Long was being questioned by John. John had released Dr. Long, who trapped Marcie in a freezer room. Michael rushed to the hospital and confronted Dr. Long, who was carrying an organ cooler. This cooler contained a donor heart that was meant for Viki. Dr. Long and Michael fought on the rooftop of the hospital and the donor heart fell out of the cooler and became contaminated. Dr. Long was going to kill Michael and Marcie, but John and Antonio arrived on the scene and arrested him.

Soon after, Marcie brought her manuscript, The Killing Club, to Michael for him to read. He encouraged Marcie to seek out a publisher, even introducing her to literary agent Hayes Barber. However, Marcie's new schedule with trying to get her book published and Michael's work at the hospital put a distance between the two, and they eventually agreed they were better friends than lovers, even though Michael still had very strong feelings for Marcie. When Michael was accused of murdering Tico Santi, Marcie helped to clear his name, the same way that Michael stood by Marcie when she was hit with a car driven by Margaret Cochran.

Overcoming difficulties from Michael's demanding hospital job and Marcie's newfound fame as an author, Marcie and Michael cemented their relationship and married on May 5, 2006. 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.

After several months of being on the run, Michael McBain figured out that Marcie was in Paris, Texas. Viki by this point also had come face to face with Marcie, who held Viki hostage inside the Bon Jour 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 to learn that the child she had prepared to receive was now dead. Michael comforted her during this time and said he had left her during the pregnancy but wouldn't leave her now.

An autopsy performed on the dead baby revealed that the cause of death was RH disease, which Michael explained sometimes occurs when a baby's mother and father have different blood types. Although it's rare for the disease to occur in first births, no one questioned the findings. Michael and Marcie moved back in together and tried to get on with their lives. In March 2009, Michael was at the center of action at the hospital when a car accident occurred involving Cole Thornhart, Matthew Buchanan, and Gigi and Shane Morasco. Blood tests on Cole showed he was under the influence when he got behind the wheel and almost ran into the Morasco's. Marcie happened to see the blood tests and realized that Cole and Starr have the same blood type, meaning that Hope couldn't have died from RH disease as they were told. She told Michael, who had additional blood tests conducted but they all came up the same. Michael said the only way to find out how the baby really died would be to exhume the body, but Marcie talked to Starr and they agreed not to do that. Little did any of them realize that Natalie Buchanan and her fiancé, Jared Banks, had stumbled on the truth themselves and realized that the baby Jessica was raising as Chloe 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. About a month later, Michael returned to Llanview briefly to help Gigi and Rex expose Gigi's scheming sister Stacy and told Gigi that he and Marcie were happy in Seattle and preparing to become parents.

In November 2009, Michael was working at Seattle Grace Hospital when a very pregnant Marcie arrived, having just returned from celebrating Hope's first birthday in Llanview. They were both surprised to see Matthew Buchanan at the hospital, ready to undergo a risky surgery Matthew hoped would restore the use of his legs following a tragic accident earlier that year. Michael learned from Matthew's parents Bo and Nora that he had ran away from boarding school in London, and Marcie faked going into labor to try to buy time for Bo and Nora to arrive in Seattle. Matthew ended up going into surgery anyway, and Marcie then went into labor for real. With Michael by her side, Marcie gave birth to a 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.