Mac arrived in Port Charles on Valentine's Day in 1991, on a ship owned by the Quartermaines, called the S.S. Tracy. The ship had trouble docking into the Port Charles harbor due to engine problems as well as protesters causing a scene. When the ship caught on fire after an explosion, Mac jumped into the water. He was dragged out by Police Commissioner Robert Scorpio, Mac's older brother. The pair had been estranged for years, and they had not parted on good terms. Robert accused his brother of being a killer, and he suspected Mac of having something to do with the ship's engine problems.

Mac's problems with Robert got worse when several failed attempts on Robert's life pointed to Mac as the prime suspect. Mac was forced to hire Scott Baldwin to represent him. It was later revealed that the brothers' estrangement stemmed from a tragic incident when Mac and Robert's parents -- and Robert's fiancée, Lily -- were killed in a plane crash. Robert blamed Mac for being careless and trying to impress their father with Mac's piloting skills. Robert had also been seriously injured in the crash, and he thought that Mac had left him to die. In truth, Mac had gone for help, but Robert had already been rescued by the time Mac had returned with help.

Mac managed to escape from jail when an earthquake hit Port Charles. Robert found Mac trying to leave town on the next ship heading out. They had an altercation, and Robert knocked Mac overboard. Mac was later presumed dead. Robert was filled with remorse.

Later, Robert was lead into a trap in the Finger Lakes area of New York where he reunited with Mac. They realized that they had been set up by someone who had hired Mac to make an appearance in Port Charles. Robert was shot, and Mac helped him get medical attention. Mac donated blood for a much-needed transfusion that saved Robert's life.

The brothers patched up their differences, and Robert learned that Mac had never abandoned him following the plane crash. Robert convinced Mac to head back to Port Charles and clear his name. Mac confessed his crimes to Robert and revealed the name of the person who had hired him. Anna Devane, Robert's wife, managed to find the brothers after they had escaped from the county jail. The trio hid out in a mansion in Finger Lakes from the local sheriff who didn't believe Robert and Mac's story regarding the death of the man who had tried to lure them to their deaths. Dominique Taub, who owned the mansion, invited the three to stay, and she took a shine to Mac right away. Dominique turned out to be deaf and very married. Despite that, Mac was drawn to her, and he hid her in Port Charles from her abusive husband.

Mac decided to put roots down in Port Charles, so he opened a club called the Outback. Dominique's childhood nanny, who had recently arrived, was murdered on opening night. Dom was charged with the murder, and her husband managed to obtain legal guardianship of her. Mac got beat up trying to help Dom escape then Dom's husband carted her off to make an heir. Dom escaped then made her way back to town, but she was hit by a car and found once again by her husband. Mac decided to help Dom stage her suicide then made plans to flee the country with her. While in hiding, Dom couldn't make love with Mac because it triggered flashbacks of the abuse that she had suffered at the hands of her husband.

Caught once again by Leopold, Dom was put into Shadybrook where Mac secretly visited her. Her therapist informed them that Dom would need lots of therapy before she would be capable of a real relationship with Mac. While Dom worked on getting better, Mac helped Robert and Anna in their fight against the cartel. After the cartel was defeated, and the members were sent to prison, Dominique was finally free to be with Mac. Leopold had been a member of the cartel, and he had been killed during a prison escape.

Mac taught Dominique that a man could be gentle and kind, and they fell in love. However, Mac's relationship with Dom became strained when Robert was killed in a boat explosion, while trying to save his Anna. Mac was heartbroken, but he had to remain strong for his niece, Robin. Mac's focus shifted to raising his young grieving niece, which left little room for Dom. Mac broke up with Dominique when he realized that he couldn't love her the way that she wanted him to.

In 1992, Mac used his private investigative skills to help Felicia Jones unravel a mystery. Mac hired her as a bartender at the Outback and helped her uncover the root of her recurring nightmare, and some missing time. Eventually, Felicia realized that the nightmare had been a repressed memory of a real murder. Felicia had met a man in Texas and fallen in love with him before discovering that he was married. Felicia had witnessed Ryan Chamberlain murder his wife when she had confronted Ryan about his affair with Felicia.

Felicia's memories had returned during a violent confrontation with Ryan. A short time later, Mac found Felicia standing over Ryan's body. She had stabbed Ryan in self-defense. Felicia was charged with attempted murder and sentenced to a term in a mental hospital. Mac rescued her and they went on the run from the law. They began digging into Ryan's past and faked Felicia's death to throw Ryan off their trail. After discovering that Ryan had committed several murders, they tricked Ryan into confessing on tape. Eventually Ryan was apprehended and convicted of murder.

Mac and Felicia grew closer, but they tried to fight off their attraction. They failed miserably, so they agreed to go slowly and date. Mac fell in love with Felicia, and he asked her to marry him. However, the timing was off because they were in the middle of trying to catch Ryan who had managed to escape. Felicia also had reservations because of her failed marriage to Frisco Jones.

In 1994, after Ryan had nearly killed her, Felicia realized that she loved Mac, and she proposed to him. He said yes, and they celebrated by making love for the first time. They planned their wedding, and they became partners in a private investigation business. Unfortunately, their wedding was ruined when Ryan once again escaped, and he assumed his twin brother's identity. Ryan went to the church with a bomb, and Mac struggled with him. Mac was injured and they had to postpone their wedding.

In the end, Mac and Felicia didn't exchange vows. Felicia's young daughter Maxie fell ill and was in need a heart transplant. Mac found Maxie's father Frisco in Africa and convinced him to return to Port Charles. Mac saw that Felicia had unresolved feelings for Frisco, so he ended things with Felicia. Despite the breakup, Mac and Felicia remained good friends.

That friendship was tested when Felicia revealed that she was pregnant, but it was Frisco's baby. Frisco had once again abandoned his family, but Mac was there for Felicia's daughter, Georgie, and he remained close to Felicia's elder daughter, Maxie.

Shortly afterwards, Mac became romantically involved with Katherine Bell. They nearly broke up months later when Lucy informed Mac and Damian Smith that Katherine had been seeing both of them. Lucy was retaliating for Kevin and Mac dressing in drag in order to prove that Madame Maia, Lucy's psychic, was a fake. Mac was hurt, but Katherine sweet-talked Mac into giving her another chance.

Mac and his niece Robin began to butt heads over her new flame, Stone Cates. Mac wasn't pleased that Stone lived with local mobster Sonny Corinthos. After Robin gloated to Mac about sleeping with Stone -- despite Mac's attempts to keep the teens apart -- Felicia advised Robin to go on a birth control pill. Assuming that she was safe, Robin slept with Stone without using a condom.

Weeks later, Stone began to complain of severe headaches and a cold that wouldn't go away, prompting Kevin to order a round of blood tests. The tests revealed that Stone was HIV positive. Stone couldn't bring himself to tell Robin, but he was forced to speak up when he was shot, and she attempted to help him. At the hospital, Alan Quartermaine persuaded Robin to be tested, but she was negative.

Alan also had the grim task of informing Stone that Stone was in the advanced stages of AIDS. Stone started drug therapy immediately, and he pushed Robin away out of fear that he would infect her. When Robin broke the news to Mac that Stone had AIDS, and she'd had unprotected sex with Stone, Mac was furious. However, Mac grew to accept Robin's feelings for Stone. At a surprise party for Stone, the guests presented Stone with the memory book that Robin had initiated. In the book were several letters written by Stone's friends, including a touching one from Mac.

In late 1995, Stone's health declined. Alan discovered that Stone had lymphoma. Stone chose to forego treatment, and his friends rallied around him during his last few weeks of life. Near the end, Stone insisted that Robin get tested again. This time the test confirmed that Robin was HIV positive. Mac was very loving and supportive of her, but Stone was devastated. Mac and Sonny took turns watching over the star-crossed lovers, and Stone quietly died. His memorial service was held at Sonny's penthouse, and Mac had an AIDS memorial quilt made in Stone's memory, which was presented at the first annual Nurses Ball to raise money for AIDS research.

In 1996, Mac became the police commissioner of Port Charles. He focused on cleaning up police corruption, but he was also in a position to help Felicia with the various cases that she took on as a private investigator. One case involved a woman named Tess who was eager to find her missing husband who had vanished years earlier. Felicia noticed an uncanny resemblance between Mac and the man in the picture that Tess had provided.

Later, Mac discovered that Tess had tried to set him up to take the fall for the assassination of his old foe, Jasper Jacks. Tess was apprehended. Mac and Felicia had a predicament. Felicia had accepted a marriage proposal from the fake "Mac," a man named James Meadows, and Mac and Felicia didn't have the heart to tell their friends that her engagement to Mac was not real.

Mac and Felicia pretended to be engaged, and they ended up falling in love all over again. Mac professed his love to Felicia at the altar of their double wedding with Lucy Coe and Kevin Collins. Lucy and Kevin decided to call off their wedding, so that Mac and Felicia could have the special day to themselves. Felicia shared the whole story involving Tess, James, and the fake engagement with the congregation before exchanging vows from the heart with Mac. They celebrated with their family then flew off to Paris for their honeymoon.

Mac and Felicia were happy for a time raising the girls and settling into life as a family. However, cracks in the marriage began to develop when Felicia decided to write Lila Quartermaine's memoirs then enlisted Luke Spencer's help. Luke have been grieving over his son's presumed death in a fire. Luke and Felicia began to grow close, while Mac found himself tangling with his brother's nemesis, Cesar Faison. After months of taunting Mac by approaching his loved ones, Faison kidnapped Felicia. Both Luke and Mac went looking for her, but Luke was the one who had found Felicia.

Luke was captured, and he and Felicia nearly made love, while they were trapped, but they stopped before anything happened. Unfortunately for both, Faison had taped their encounter, and he later sent the video to Mac in time for Christmas 1999. Mac was devastated by the video, and he confronted Felicia. Mac forgave Felicia for the transgression, and the two were determined to save their marriage.

Unfortunately, Felicia was unable to keep her promise, and she left town with Luke to help him find his son, Lucky Spencer. Fed up, Mac filed divorce papers as well as a petition of custody for Maxie and Georgie. He later dropped the custody petition, but he proceeded with the divorce. Mac let his bias interfere with his job when he railroaded Luke into a murder charge knowing that the evidence was circumstantial.

Before the divorce was finalized, Felicia returned from a vacation with the girls and confessed that she still loved Mac. Mac's joy was short-lived when Felicia took the stand to testify on Luke's behalf when it appeared that Luke might be found guilty of murdering Stefan Cassadine. Felicia revealed that she and Luke had been in a motel making love on the night of Stefan's "murder." Mac was devastated. He was also humiliated when it was discovered that Stefan had faked this death. Mac resigned as police commissioner and went back to private investigation.

After realizing that he still loved Felicia, he vowed to her that he would win her back from Luke. But he soon realized that she was in love with Luke. Felicia tried to have a deeper relationship with Luke, but Luke was too wrapped up in other things to notice. Heartbroken, Felicia took the girls to Texas for a while.

In 2001, Mac returned to his job as police commissioner in the midst of an investigation into mob boss Joseph Sorel's murder. There were several suspects, and a few tried to implicate others. After several twists and turns, Mac enlisted Felicia's help to hunt down the murderer. Mac gathered all the suspects in an old mansion, and eliminating them one by one, Mac and Felicia figured out that Sorel's daughter Angel had killed her father. Mac went to arrest her, but Jax, Sonny, Carly, and Angel had arranged for Carly and Angel to switch places. By the time Mac caught up to his suspect, Jax had already put Angel on a plane headed out of the country.

As the Spencer/Cassadine war reached a boiling point, Gia Campbell tried to get Mac to arrest Stavros Cassadine/Lucien Cane. He refused since she had cried wolf on several occasions. But when Helena and Stavros were finally defeated in Helena's underground lab, Mac was right there to arrest Helena. To everyone's dismay, Mac wasn't able to find any physical evidence of Helena's latest evil actions, including Stavros' resurrection. Later, Helena escaped, and Mac clashed with Luke on how to handle the search for her. Luke caught Helena and brought her back to the police. Mac gave permission for Luke to accompany Helena to the prison van to make certain that she didn't escape again.

In 2002, As Luke and Laura Webber prepared to remarry, Laura began to have flashbacks of a night long ago in the garage attic of her childhood home, which belonged to the Scorpios. One night, a fire broke out in the attic, while Maxie was watching Lulu. Mac was horrified when he discovered that the fire had been deliberately set, so Luke urged Mac to talk to Scott Baldwin because Scott had been the first on the scene. When Rick Webber, Laura's father, was killed in a drunk-driving accident, Mac and Scott realized that the accident had been staged. Mac and Scott suspected that Lucky and Nikolas had been responsible for moving Rick's body, they thought Luke had actually killed Rick in the attic. Mac arrested Luke, while Laura was admitted to the hospital for mental evaluation because she had suffered a breakdown. In time, it was revealed that a teenage Laura had caught Rick with his lover in the attic, and things had ended with Laura striking the woman and killing her. Scott had helped Rick cover up the death, and Scott had been responsible for the fire in the Scorpio's attic. Scott had also killed Rick when he had found Rick in the attic with Laura about to inject her with something. Fearing for Laura, Scott had struck Rick. Scott had let Luke take the fall because Scott had hoped to protect Laura from the truth about Rick's lover's murder.

On November 2, 2002, Luis Alcazar died when he tumbled over the balcony of his hotel suite. There were several prime suspects as Mac investigated the international arms dealer's death. After shocking twists and turns, it was revealed that Alexis had been on the balcony with Luis when he had approached Alexis with deadly intent. Alexis had shoved Luis away, and he had stumbled backwards and over the railing.

In February 2003, Felicia went to Texas to take care of her ailing grandmother Mariah, so Mac became the primary caregiver to Maxie and Georgie. Mac had his hands full with Maxie who had grown into a rebellious teenager. Mac was a stern, but loving guardian to both girls. Soon Georgie gave Mac headaches as well by dating Dillon Quartermaine. Mac wanted only the best for Robin, Maxie, and Georgie, and he was willing to compromise. All three girls loved him dearly, and both Maxie and Georgie considered him more of a father than Frisco.

On February 6, 2004 Mac was seriously injured when a fire broke out in the electrical room of the Port Charles Hotel. Mac had responding to a report that Zander Smith had been hiding in the basement. As Mac opened the door to the room, a backdraft engulfed him in flames. Maxie rushed to Mac's side when she found out what had happened, and she tearfully confessed that she had been hiding Zander in the hotel's basement.

Meanwhile, Georgie had briefly been trapped in the hotel as the fire had raged. Georgie arrived at the hospital, and Maxie was forced to break the news about Mac to her sister. Dillon was at Georgie's side when Georgie went to see a badly burned Mac. The sisters continued to worry as Mac's condition deteriorated. Felicia returned to support her daughters as they all sat vigil at Mac's bedside. Felicia was horrified when Mac suddenly vanished, but she was able to track him down at Mercy Hospital where he'd been listed as a John Doe.

Felicia was determined to get to the bottom of things, but to her surprise Mac woke up, and he asked her to drop it because he wanted her to focus on her family. Mac made a full recovery and returned to work as the police commissioner. He also continued to help Felicia raise Maxie and Georgie, but Felicia once again left the girls with Mac to return to Texas to care for her ailing grandmother.

In early 2006, Mac received some startling news when it was revealed that Robert was alive, and he'd been working undercover for the WSB. However, Mac also had to contend with the sad news that Dillon had contracted a potentially deadly form of encephalitis, and Dillon and Georgie had decided to marry before Dillon died. Georgie was not a legal adult, so she needed Mac's consent. Mac relented because it was clear to him that Georgie and Dillon loved each other. Mac attended the intimate ceremony which took place in Dillon's hospital room. Dillon survived, but the marriage between Dillon and Georgie ended.

Around the same time, Maxie struggled to cope with the death of her boyfriend Jesse Beaudry, and she found comfort in his partner's arms. Lucky Spencer had married nurse Elizabeth Webber, and together they were raising her son with Zander Smith. However, Lucky had developed an addiction to pills, and Maxie had helped supply Lucky with the opioids in the hopes that he would leave his wife for her. Instead, Lucky decided to get clean and save his marriage. Mac was unaware of the details, but he was livid because he believed that Lucky had taken advantage of Maxie. Mac fury mounted when Maxie revealed that she had miscarried Lucky's baby when she'd fallen down a flight of stairs during an argument with Lucky.

Eventually, Maxie realized that she'd gone too far. She made a full confession to Mac about how she had supplied Lucky with pills and she had faked her pregnancy and miscarriage. Mac was disappointed, but supportive as Maxie tried to make amends and move on with her life. Mac also apologized and made peace with Lucky.

On December 17, 2007, Mac's world was shattered when Georgie was slain by the Text Message Killer who was later revealed to be Georgie's friend, Diego Alcazar. Felicia returned for her daughter's funeral, but Maxie leaned on Mac. Felicia explained that she had put her grandmother in a nursing home then Frisco had called asking for Felicia's help with a World Security Bureau assignment, but Maxie wasn't satisfied with Felicia's excuse for the extended absence because Maxie knew how much Georgie had missed not having a mother. After Felicia left town, Mac and Maxie helped each other through the grief over losing Georgie.

At the beginning of 2008, Mac was delighted to learn that his beloved niece Robin was pregnant with her first child. The father of the baby was a neurosurgeon at General Hospital named Patrick Drake. It took some time for Robin and Patrick to make it down the aisle, but when it was time, Robin asked Mac to step in for her father. However, Robin went into labor before Robin and Patrick could exchange vows, and she later gave birth to a baby girl that she and Patrick named Emma.

Mac was a devoted great-uncle, and a few weeks after Emma's birth, Robin and Patrick were married. This time, Robin's parents were able to make it to the wedding, so Robert gave his daughter away.

Maxie had also found love with Damien Spinelli, Sonny Corinthos' tech wizard. Mac didn't like the quirky young man, and he objected to Spinelli working for the mob. Despite Mac's objections, Maxie accepted Spinelli's proposal, but Maxie kept getting cold feet even though she deeply loved Spinelli.

Although Robin and Maxie were each involved in romantic relationships of their own, they joined forces with Molly and Kristina Davis to fix up Mac and Alexis. Mac and Alexis had remained cordial throughout the years, so they played along for a while. Mac and Alexis exchanged a few kisses, but sparks didn't fly. They enjoyed each other's company and remained friends. Mac did enjoy a one-night stand with Diane Miller, but her heart belonged to Max Giambetti.

Mac remained the police commissioner, but there had been some serious missteps over the years. In 2006, mobster Many Ruiz took Maxie hostage during a shootout with the police. Dillon was shot, and Maxie was later rescued. Two years afterwards, shots were exchanged and another situation at the police station almost ended in a hostage crisis. In 2010, Mac was shot when Warren Bauer, a grieving father, snapped and decided to confront Kristina Davis with a gun because he blamed her for Kiefer's death.

In early 2012, Detective Ronnie Dimestico was revealed to have been targeting strippers, and he had kidnapped Lulu Falconeri and Sam McCall. After Ronnie was shot and killed, it was revealed that Ronnie had been attacking women for years because his unfaithful wife had left him for another man. The scandal forced Mayor Lomax to fire Mac because she had lost faith in his ability to run the police department.

On February 21, Mac's world was rocked once again when his beloved niece Robin was presumed killed in a lab explosion. Unbeknownst to Mac and the rest of Robin's family, Victor Cassadine kidnapped Robin and used her medical knowledge to aid him and Helena Cassadine with their newest plot to wreak havoc on Port Charles.

Mac grieved for Robin, and he grew closer to her daughter Emma. On April 27, Felicia returned to town to support her daughter when Maxie was accused of killing Lisa Niles. Maxie hadn't killed the diabolical doctor, but she had been willing to go to prison for the crime to protect her new husband Matt Hunter. Maxie had been deeply grieving Robin's passing, and she felt that her life was over. Felicia was stunned when Maxie was sentenced to twenty years behind bars. However, Matt was consumed by guilt, and he confessed to the murder in a few weeks after Maxie's sentencing.

Mac wasn't happy that Felicia had returned because he feared that she would leave again, but Felicia was determined to prove to both Mac and Maxie that she was there to stay. She was supportive when Maxie announced that she intended to be a surrogate for Lulu and Dante Falconeri, and she was instrumental in getting Mac to accept Maxie's decision. In time, Mac and Felicia began to date again, and Mac took a job bartending at the Floating Rib.

Felicia reached out to her ex-husband to let Frisco know about Maxie's plan. On February 5, 2013, Frisco returned to Port Charles. Mac was not happy, especially when Frisco made it clear that he wanted to rekindle things with Felicia. Two months later, during the annual Nurses Ball, Frisco proposed marriage to Felicia, but she turned him down because she was in love with Mac. Mac happily accepted Felicia's proposal of marriage. Maxie was happy for Mac and Felicia, but she was crushed when her father decided to return to work for the WSB.

On August 16, Mac and Felicia exchanged wedding vows, with Spinelli and Maxie standing in at the last minute for Duke Lavery and Anna Devane as best man and matron of honor.

A few months later, in November, Mac was shocked to learn that Robin was alive when she showed up during Patrick and Sabrina Santiago's wedding. Sabrina was left heartbroken -- and pregnant -- when Patrick went back to Robin. Mac happily reunited with his niece, but it wouldn't last for long. Victor Cassadine threatened Robin's family if she refused to continue working with him. He forced her to walk away from her family without revealing the truth about her mission. Robin left town for a while, but she maintained contact with her family until she could break Victor's grip on her.

Meanwhile, Mac and Felicia settled into married life. They bought the Floating Rib, and together they ran the restaurant and bar. They were also supportive when it was revealed that the baby that Maxie had given birth to was Maxie and Spinelli's daughter. Maxie had miscarried Lulu and Dante's baby, so she had hoped to pass off her and Spinelli's baby as theirs. Spinelli sued for and won custody of little "Georgie" then moved to Oregon with his new girlfriend, Ellie Trout. Heartbroken, Maxie left town to figure things out, but she returned a few months later with a man named Levi Dunkleman.

Mac disliked Levi from the onset, but he was happy for Maxie because she appeared to be in a better place. However, Levi turned out to be a jewel thief named Peter Harrell Jr. who was after Felicia's Azetc jewels. On Levi and Maxie's wedding day, Levi and his accomplice took both Maxie and Lulu hostage, but Dante and Detective Nathan West rescued the two women. When the dust settled, Levi was dead.

Maxie returned home, and she picked up the pieces. In time, she found love with Nathan. Robin had also returned to town. Robin and Patrick remarried then packed up their daughter and moved to Berkeley to make a fresh start. Mac was disappointed, but he gave Robin and Patrick his blessings.

On January 17, 2017, Maxie and Nathan were married. Mac approved of the detective and gave the couple his blessing. In July, Robin gave birth to a baby boy named Noah Robert Scorpio-Drake. In November, Mac and Felicia were overjoyed when Maxie and Nathan announced that they were expecting. However, tragedy struck a few months later when Nathan was shot and killed in the line of duty trying to save Maxie from his gun-wielding biological father -- Cesar Faison.

Mac and Felicia took care of their daughter as she grieved her husband. On May 21, 2018 Maxie gave birth on the side of the road to a baby boy named James West. Peter August, Nathan's paternal brother helped deliver the healthy baby boy. Mac was not thrilled that Maxie had befriended Peter because he feared that Peter was a chip off of Cesar's back. Peter respected Mac's reservations, and he tried his best to prove himself to Mac. Mac was a doting grandfather to James, and he was very protective of Maxie.

Mac was also a devoted husband. He and Felicia enjoyed married life. When Lulu decided to do a series for the Invader about Ryan Chamberlain on the anniversary of the serial killers death, Felicia agreed to an interview. Mac was not pleased because Felicia had been having nightmares, and she had taken to sleeping with a bat next to her. He worried that dredging up the memory of the serial killer who had stalked her would cause Felicia more pain.

In March 2019, it was revealed that Ryan Chamberlain was alive, and he'd been posing for months as his twin brother Kevin Collins, while Kevin had been locked up in Ferncliff. Mac was furious when he confronted Kevin because he accused Kevin of jeopardizing everyone by hiding Ryan in a sanitarium rather than handing Ryan over to the authorities. When Ryan was presumed dead after falling into the Niagara River, those who knew Ryan best were certain that Ryan had once again faked his death. Mac, Felicia, Ava Jerome, Kevin, Laura Webber-Collins, and Lulu teamed up to lure Ryan out of hiding. The plan was a success. In June, Ryan was captured.

On June 17, 2019, Laura, who had been sworn in as mayor months earlier, asked Mac to step in as interim police commissioner until Jordan Ashford recovered from a kidney transplant. Mac agreed to take over the position, but he made it clear that it had to be temporary. The following day, Robert announced that the WSB no longer required his services effective immediately.