Michael was conceived in 1997 but his mother Carly was not sure who had fathered her child. She hoped that the man she cared for, Dr. Tony Jones, was the father and allowed him to believe that the child was his. However, Michael's conception was the result of Carly's one night with A.J. Quartermaine. A.J. struggled with alcohol and initially did not remember his night with Carly. Eventually Carly's relationship with Tony fell apart and A.J. realized that could be the father of Carly's unborn child. She claimed that A.J.'s brother Jason Morgan was the father of her child and he agreed to go along with her lie.
When Michael was born, he required immediate heart surgery and Jason made the necessary medical decisions on Carly's behalf. Carly struggled with postpartum depression and left town shortly afterwards. Jason cared for Michael in her absence and named him Michael after his good friend Michael "Sonny" Corinthos. Jason continued to bond with the child and grew to think of himself as Michael's real father. Jason's girlfriend, Robin Scorpio, helped Jason care for Michael although she believed it was wrong for A.J. to be denied the chance to know his child.
Carly recovered and returned home briefly to care for her son. However, she had to leave Michael with Jason and Robin once again. Tony was devastated when he learned that he was not Michael's father and kidnapped the baby. When the court was lenient with Tony's punishment, Carly took matters into her own hands and fired a shot at Tony. She was sent away for psychiatric care.
Eventually Robin revealed the truth of Michael's paternity and Michael's parents, Carly and A.J., were married and they lived together in the Quartermaine mansion. The marriage quickly fell apart and Carly moved on with Sonny Corinthos. Sonny forced A.J. to sign away his legal rights to Michael and Sonny became his adoptive father. Carly and Sonny embarked in a tumultuous relationship that included several marriages and divorces to one another. In the process, Michael gained a half-brother named Morgan from Carly's relationship to Sonny and an adoptive half-sister named Kristina through Sonny's tryst with Alexis Davis.
As a young child, Michael was exposed to the dangers of Sonny's life in the mob and he grew up surrounded by body guards. In February of 2005, an enemy of Sonny's named Faith Roscoe kidnapped all three of Sonny's children, including Michael. As the oldest, he tried to protect his younger siblings until they were separated. Faith's accomplice in the kidnapping was Michael's biological father A.J. and Michael was delivered to him. He brainwashed Michael to believe that Carly and Sonny did not want him.
Jason tried to rescue Michael from A.J. and the men fought. During the scuffle, A.J. fell and broke his back. While A.J. was in the hospital, someone smothered him and he was presumed deceased. Michael started to have nightmares and imagined that he was the one who had killed his biological father. After therapy, he realized that he had only witnessed the crime. Asher Thomas, who A.J. had blackmailed, had done the deed.
Michael recovered from his time with A.J. and continued to emulate Sonny as he grew older. When the Text Message Killer was on the loose in 2007, Michael illegally purchased a gun to protect his family. However, when his father's fiancée Kate surprised him at the waterfront, he accidentally shot her. Kate survived, but Michael ran away from home. Michael eventually agreed to meet his mother at the warehouse that Sonny's enemies had wired with explosives. Carly and Michael were there when it blew up, but both recovered.
Michael's parents remained concerned over his interest in the mob. After Sonny stepped down and turned the organization over to Jason, Michael accompanied his father on a trip to the coffee warehouse to see the legitimate side of the business. However, mob rival Claudia Zacchara and hired sharp shooter Ian Devlin used the opportunity to take out Sonny but the bullet ricocheted and hit Michael in the head. He was rushed to the hospital and ended up in what was believed to be a permanent coma. Michael was sent to a long-term care facility in May 2008, where he remained comatose for nearly a year.
Neurosurgeon Patrick Drake performed a controversial experimental operation that got Michael out of his coma. Michael was shocked to discover that Sonny had married Claudia, who was pregnant with Sonny's child, and that Carly was pregnant by Jax. Michael struggled with his emotions and became enraged with driving. He thought that he had run Claudia off the road, which caused her to miscarry. Michael ran away to Mexico but Kristina tagged along. Kristina admitted that she had caused the accident and Jason, along with Kristina's sister Sam, brought them back home.
Michael bonded with his step-mother Claudia until he remembered that while he had been in his coma, she confessed to ordering the hit on Sonny and hiring the shooter which had resulted in Michael's injury. When Sonny learned the truth and publically confronted Claudia, she kidnapped a very pregnant Carly. Michael was the first to find the women and discovered that his mother had given birth. He heard Carly beg Claudia not to take her daughter. Michael burst in through the front door and saw Claudia holding his baby sister. He reacted by grabbing an axe handle and striking Claudia. The blow killed her instantly.
Michael's family agreed to cover up Michael's role in Claudia's death and Sonny went to trial for her murder. Michael was wracked with guilt and eventually told his long-lost older half-brother Dante the truth. As a police officer, Dante believed it was his duty to reveal the truth but assured Michael that the court would go easy on him. However, the judge was angered by the cover-up and gave Michael a harsh sentence in Pentonville prison.
To protect Michael from Sonny's enemies in prison, Jason made a deal with the prosecutor and confessed to criminal activity so that he could be sent to Pentonville, with the proviso that he's share a cell with Michael. Soon thereafter, Dante pleaded with the judge to show lenience, and the judge capitulated. He had Michael released into Dante's custody.
Although Michael was released, he was on parole and was ordered to have minimal contact with his father and required to reside with Dante. His family wanted him to finish high school but felt that he had nothing in common with his classmates and that they would not be comfortable around someone that had committed murder. Michael was more convinced than ever that he should work for his father so that he could eventually take over as his successor.
Michael did return to school after he was reminded of how much his sister needed him. She also felt like an outsider after the death of her abusive boyfriend. Michael did well in his classes, but he struggled to interact with his classmates. He was involved in a fight his first day, and he pulled away when one of Kristina's friends touched him flirtatiously.
Even though Michael agreed to finish high school, he remained interested in his father's organization and tried to prove he could be an asset to the business. When Michael overheard his father confess he had planted the bomb in Johnny Zacchara's car that almost hurt Kristina, he agreed to remain quiet. He told his father he understood the show of power. Michael tried to broker peace between the Corinthos and Zacchara organizations. While he spoke to Johnny, a car opened fire on them. Michael pushed Johnny out of the way. When the police arrived, Dante covered Michael's involvement so he would not be found in violation of his parole.
In the time after Michael was released from prison, he was easily startled and reluctant to have physical contact, and he suffered nightmares. Michael refused to open up about his experience but talked to Jason about sex and asked to be set up with a prostitute. Jason refused but Sam overheard the conversation and agreed to set Michael up with her friend Abby.
Abby's professional stripper name wad Candy, and Michael had a violent reaction when Candy tried to touch him. She forgave Michael for his reaction and they developed a friendship which later turned in to a relationship. Michael remained hesitant to have physical contact with Abby, but she was fine with taking time to get to know one another. He defended Abby to his mother after she learned that Abby had been a prostitute and asked Dante to help clear her name after she was arrested.
Michael witnessed Abby being attacked by her ex-boyfriend, Brandon. Initially Michael froze because he was paralyzed by the memories of his attack in prison, but he stepped in to protect Abby. If Michael had not intervened, Abby believed Brandon would have raped her. Michael told Abby he recognized her fear because Carter had raped him in prison. Abby's acceptance gave Michael the strength to tell his mother and Jason about his rape. He agreed to attend counseling, but Michael did not want his father to learn what had happened to him. When Sonny learned of the rape, he assured Michael he loved and respected his son as much as he ever had.
Abby was Michael's date when his father married Brenda Barrett. Chaos erupted at the wedding when a limousine blew up with Sam inside, and Brenda was kidnapped. A European mobster named the Balkan was behind the bomb and the kidnapping. Michael went after one of the Balkan's men. The man had a gun, but Dante arrived before the man fired a shot. Michael remained determined to work in Sonny's organization. He showed up to unload an illegal shipment. The police arrived, but Jason removed Michael before he was arrested for violating his parole.
Both Jason and Sonny continued to rebuke Michael's attempts to join the organization. Michael found empathy in Johnny Zacchara, and they discussed what it was like to enter into the family business. Johnny told Michael he could have a place in the Zacchara organization without going against Sonny or Jason.
As Michael considered Johnny's offer, Abby's ex-boyfriend Brandon was released from jail and beat Abby once again. Shortly after the confrontation, Brandon was found dead. Michael and Abby were both suspects in the murder until Johnny realized that his father, Anthony Zacchara, had arranged for Brandon to be released on bail and then hired a woman who looked like Abby to kill Brandon. Michael teamed up with Johnny to find the woman that had killed Brandon. After the charges against Abby were dropped, Michael agreed to work for Johnny. Everyone close to Michael, including Abby, disapproved of his decision.
High school graduation day arrived for both Kristina and Michael. Although Michael never applied, he was accepted at Port Charles University. Kristina had applied on his behalf. Michael moved in with Abby and considered his summer job offers. Sonny, Jax, and Johnny all offered Michael summer positions. Michael turned them all down and instead chose to work for Edward at ELQ because Edward had offered Abby a position as well. Abby enjoyed her work at ELQ, but Michael did not feel the same way and quit shortly after.
Around the same time, Carly blocked Sonny from seeing Morgan after she accused Sonny of causing a plane crash that resulted in Jax's presumed death. Michael sided with his father instead of his mother and he decided to step in to help him out in the business. Michael took over as the manager of Sonny's warehouse, although he remained interested in the illegal aspects of the business. Michael tried to prove to Sonny that he was mature enough to do more than manage the legitimate parts of the organization after he found Dante unconscious in the warehouse after being shot. Michael wanted to investigate what had happened and was disappointed when Sonny allowed Shawn to deal with the matter instead.
Michael was hurt that Sonny continued to protect him from the shady side of the business but he changed his focus to protecting Abby after several of her friends from Vaughn's were attacked. The police were unable to catch the perpetrator and Michael feared for Abby's safety. He asked Tracy to send Abby out of town on business for ELQ. Tracy agreed and Abby went to Chicago. Tragedy struck while Abby was in Chicago. She walked by a construction site and was killed when a crane accidentally dropped its load on her. Michael was devastated and blamed himself for her death.
Michael decided to spread Abby's ashes in a field of lavender in New Zealand. While on his trip, he spotted a man in the airport that looked like Jax. When Michael returned to Port Charles, he asked his mother if there was any chance Jax could still be alive. She told him Jax was gone. Michael eavesdropped on a conversation Carly had with Shawn in which she confessed her guilt over lying to Michael about the truth that Jax was still alive. Carly believed that Sonny would make another attempt on Jax's life if the truth came out. Michael was angry at Carly and he used the New Year's Eve bash she hosted at the Metro Court to publically announce that Carly had allowed everyone to grieve over Jax when she knew all along that he was alive.
While Michael continued to grieve over Abby, he chose to enroll in college and become the kind of man that Abby have been proud of. He found a companion in grief after he met a young woman named Starr Manning. Michael happened upon a car accident and tried to rescue Starr's boyfriend and daughter from the vehicle. Starr lost consciousness while Michael was unable to save her family.
As more details about the car accident came out, Michael learned that Anthony Zacchara had been driving the car that hit Starr's family. Anthony had lost control of the vehicle after two of his tires had been shot out. Anthony had refused to help Starr after the accident and he stated that he had to leave because Sonny was after him. The police considered Sonny the main suspect has he had threatened Anthony's life in front of a witness earlier that same day. Michael questioned if his father was guilty even though Sonny swore he had not caused the accident.
Michael developed a friendship with Starr even though she blamed his father for the deaths of her boyfriend and daughter. Sonny was charged with causing the accident and asked Michael to stay away from Starr. He was concerned that she would take advantage of Michael's concern for her and use it to gain information related to the trial. Michael told his father the point was moot since she had been released from the hospital and returned home.
Starr returned to Port Charles to testify at Sonny's trial and Michael allowed her to secretly stay with him. He told Starr about losing his girlfriend Abby and Starr shared what her life had been like with her boyfriend and her daughter. Starr remained convinced that Sonny had caused the accident although Michael believed that his father was innocent. Michael sat with Starr in the courtroom and they were both present when Sonny was declared not guilty. Starr maintained that Sonny was guilty despite the acquittal and Michael supported her decision to return to her life in Llanview.
However, Starr did not return home but instead took Sonny hostage at gunpoint and threatened to kill him. Michael saw the surveillance footage at his father's home and saw Starr lead his father out at gunpoint. He found them and talked Starr out of shooting his father. Afterwards, he gave a statement to the police and Starr was arrested for attempted murder. Starr begged Michael to recant his statement and explained that she now realized she needed to honor her boyfriend and daughter by making her life mean something. She swore she would not go after Sonny again but Michael refused to believe her. To Starr's relief, Sonny intervened and asked Michael to take back his statement.
Michael and Starr renewed their friendship and Starr rented an apartment which she shared with Trey Mitchell, the producer of Kristina's reality show Mob Princess. Michael was wary of Trey and did not care for the flirtatious banter he exchanged with Starr. Kristina also noticed the interactions between the roommates and the siblings discussed their feelings about Starr and Trey living together. Kristina admitted that she was interested in Trey and pressed Michael to share how he felt about Starr.
Michael insisted to Kristina that any feelings he may have toward Starr were irrelevant because she was still grieving the loss of her family. He continued to spend time with Starr and he invited her to spend the Fourth of July with him at the Quartermaine gathering. As the pair spent the day together, they gave in to their feelings and shared a kiss. Afterwards they decided to pursue a relationship and made their relationship public during Starr's singing debut at the Haunted Starr nightclub.
Michael leaned on Starr after Jason was killed and A.J. was revealed to be alive. Starr supported his decision to allow A.J. into his life and she helped him deal with the fallout from Sonny and Carly. However, A.J. became Michael's support system after Starr abruptly ended their relationship and left town. Michael threw himself into his work with A.J. at ELQ and together they searched for a newly revealed Quartermaine heir.
The heir was the daughter of Jason's twin brother Franco. Michael did not tell A.J. about his past connection to the girl's father until Franco was revealed to be alive. Franco insisted that he had never instructed Carter to rape Michael in prison and had never intended to cause him any harm. Franco produced a video of his conversation with Carter in which Franco told Carter to look after Michael.
As Michael dealt with the shock of seeing Franco alive, he confided in Morgan's girlfriend Kiki and they shared a kiss. Almost immediately afterwards, Michael learned that Kiki was Franco's daughter and his cousin. Regardless of the familial ties, Michael continued to be drawn to Kiki and the feelings were mutual. They tried to avoid one another and Michael respected Kiki's decision to marry Morgan. However, Michael's feelings changed after he learned that he and Kiki were not related because a man named Silas Clay, not Franco, was her father.
Michael was thrilled to learn that he and Kiki could be together but Morgan and Kiki had already married at the courthouse before Michael could share the news. Kiki chose to remain with Morgan but their marriage ended a few weeks later when Kiki learned that Morgan had known the truth regarding her father's identity. Afterwards, Kiki agreed to explore what she and Michael could have together.
Morgan was deeply hurt by Michael's new relationship with Kiki and the brothers engaged in a fight on the docks. During the altercation, Michael hit his head and fell into the harbor. Morgan refused to help his brother and walked away. The relationship between Michael and Morgan became more strained after Morgan chose to work with the Jerome family to take down Sonny. Meanwhile, Michael struggled to retain the peace between his two fathers after A.J. was accused and acquitted of the murder of Sonny's fiancé Connie Falconeri. Michael tried to support Sonny as he grieved while he offered A.J. his support during the trial.