Mackenzie and Katherine Chancellor were both staying at the Genoa City homeless shelter, where they met and became friends. Mac had run away from St. Louis and her mother, Amanda, and stepfather, Ralph. Later, Mac trusted Kay enough to show her a letter from Mac's mother Amanda, so Kay learned of the involvement of her son, Brock, with Mackenzie's mother. Kay later revealed that she was Mackenzie's grandmother.
They left the homeless shelter with another friend, Birdie, and returned to the Chancellor Estate together to face new co-owner Jill Abbott, known as "the witch from hell," to Mac. Jill's teenage son, Billy Abbott, returned to Genoa City, making things easier for Mackenzie. The two didn't exactly hit it off right away after Billy threw a wild party in his mother's absence to get back at Jill for grounding him. Mac was almost arrested and accused of stealing. She got out of both charges with the help of attorney John Silva and Billy's persuasion with Jill.
Kay returned alone from her search for Brock in India, where he was a missionary. Shortly afterward, Kay received a call that Brock was presumed dead. So, of course, Brock showed up and they were reunited after many years. Mackenzie, dejected by her father's "death," was missing, while Mac's new friends, Billy and his friend Raul, searched for her. Mac showed up at Crimson Lights Coffeehouse, where she met Nina McNeil. Nina persuaded Mackenzie to spend the night with her. The next morning, Mackenzie was gone when Nina returned with Billy and Raul. Mackenzie showed up at the estate to get her things, intending to leave town, when her father walked in and they were finally united.
Raul and Mackenzie became close while Billy looked on, dealing with his own feelings for Mac, which she did not realize. One evening J.T. invited everyone to a party at a house where he was house-sitting. Raul showed up in time to save best friend Billy's life when Billy suffered alcohol poisoning and collapsed in the snow, as neither Brittany nor J.T. was willing to call 9-1-1 and get themselves in trouble. At that time, Mackenzie and Billy did not get along at all. But she stayed at his bedside and prayed that he would be all right.
Then came the Junior Prom where Billy and Brittany were supposed to be a shoe-in, but when the votes were counted, Billy and Mac were crowned king and queen. Only then, when they danced together at the prom, did they realize how much they cared about each other. Unfortunately Jill noticed, too, much to her horror that her son could be smitten with Kay's granddaughter. Billy showed up at the Chancellors' later, and he and Mac told each other how they felt, and kissed. Jill began threatening to find runaway Mac's mother if she became involved with Billy. So Mac and Billy began meeting in secret in the Abbott children's old playhouse. He gave her an opal ring to seal their love.
Billy, Brittany, Raul, and Rianna were chosen as the Glo by Jabot Kids as a promotion for the new Jabot teen line. Mac assisted Phyllis Summers with running the website featuring the kids. Brittany discovered that her boyfriend, Billy, was involved with Mac, so arranged for Mac to walk in on her and Billy "making love." Billy was drugged and Britt was faking it, but Mac believed what she saw and it broke her heart. Billy tried to defend himself, but couldn't remember what happened.
Local bad boy, J.T., spilled it that it was setup for Mac to see, but no one realized that Billy was drugged. Brittany was hurt, but eventually took Billy back. Raul found out, and split up with Mac, moving on to Rianna. Mac and Billy began being drawn to each other again, but it wasn't until Jack arranged for Billy and Mac to be trapped in an elevator at Jabot that they realized that they truly belonged together. Although Billy did his best to be a jerk to turn Mac away for her "own good," they eventually reconciled and became a couple again. Jill made peace with it, once she realized what a bad choice Brittany was for Billy.
Afraid that Mac's mother, Amanda, would show up in Genoa City and take Mackenzie back, Katherine petitioned and was awarded legal custody of Mac. That eased Mac's fears of discovery, and she agreed to join the on-screen Glo by Jabot Kids. When Amanda did show up, Mac rebuffed her and sent her away. But Amanda had divorced and run away from her husband, Ralph, too, and was living at the same homeless shelter where Mac and her father were volunteers. With her boyfriend Billy's help, Mac and her mother accepted each other in their lives again.
Things went fine for Billy and Mackenzie for several months. He helped her admit that she ran away from St. Louis because her stepfather, Ralph, had molested her, and her mother wouldn't believe it. Senior year began, and a holiday series on the Glo by Jabot website added J.T. and Mac to the Glow Kids. The scene changed to Jabot where a boutique opened, which was run by the kids. Phyllis had taken a job with Brash & Sassy, so a new Webmaster, Sean Bridges, was hired. Mac was in her senior year of high school, and was sending out college applications.
After the holidays, Billy realized that he was ready for more from his relationship with Mackenzie. When he shared his feelings with her, he tried to avoid pressuring her, but couldn't accept her insistence that she was not ready and should wait. As a result, the two of them broke up. They got over the trauma and became friends. Then Mac's stepfather, Ralph, showed up in Genoa City and began stalking her. He coerced Mac's mom, Amanda, into helping him steal from the Chancellor Estate. Amanda let him into the mansion while all were at the prom, but Mac returned home unexpectedly and, much to her horror, was met by Ralph.
Billy arrived on the scene as Ralph was about to molest Mac again, confronted him, and whacked Ralph over the head with a fireplace poker. Thinking he had killed Ralph, Billy took Mac to hide out in their special place, the old Abbott playhouse. Thinking they were doomed, Billy and Mac realized they still loved each other. Ralph kidnapped Kay after she returned from chaperoning at the prom, and tied her up in a motel room. Ralph, disguised as a cop, talked Raul into telling him places where he might find Mac and Billy.
Meanwhile Larry Warton found and rescued Kay. Ralph showed up at the playhouse, too late, but found the kids at a campsite where Raul and Billy used to play as kids. Ralph knocked out Billy by whacking him over the head with a rock and grabbed Mac, but our hero, Larry, showed up in time to rescue her. Larry and Ralph fought, and just before the police arrived, both ended up going over a cliff to the lakeshore below.
The next morning Ralph came to and tried to kill an unconscious Larry with a rock. Scared away by the arrival of the police, Ralph disappeared into the bushes. Larry recovered with minor injuries and major thanks from Billy's mother, Jill, for saving her son's life. Because Jill had video evidence that Amanda had stolen her jewels, and after Amanda nearly got both her own daughter and Jill's son killed, Amanda agreed to leave town if Jill would drop the charges.
After all he went through that summer, Billy decided he needed to do more with his life than go to college, so he left for Louisiana to help Mac's father, Brock, build houses for the poor. He and his mother, Jill, shared a tearful parting, although Jill felt he was making a mistake. Mac and Billy parted tearfully, as well, declaring their love and promising each other that it was not the end of them.
Mac left Genoa City that fall to attend Northwestern University. Both Billy and Mac returned to Genoa City for Christmas, and decided to attend GCU where they share a loft apartment with Raul and Brittany. By spring, Billy had proposed and Mac and Billy were to be married, with Raul Gutierrez as best man and Colleen Carlton as maid of honor. But with the reveal that Billy's mother, Jill's, actual birth mother was Katherine Chancellor, their lives were shattered when they realized they were cousins. Mac and Billy both left town on their own, devastated by the news.
Mac returned to Genoa City after spending time in the Southwestern U.S. helping out teaching kindergarten and preschool children on an Indian reservation. Her grandmother, Katherine, who had fallen off the wagon, was thrilled to see her. Mac found it difficult to live in the same house as a drunken Katherine and Jill, who hated her, so she moved back into the loft apartment with J.T., Brittany, and Raul. Kay had since become sober again,
Victor Newman, as part of his community service sentence for commercial bribery, was restoring an old building into a recreation center in a seedy part of town. He hired Mac as his supervisor on the project. 20-year-old Mac began to get close with Daniel Romalotti, who had a similar parentless background. But J.T. was only too glad to spill Daniel's secret that he was only 16 to Mac, and Mac called it quits. Mac began dating J.T., and Raul moved out of the loft to attend Pemberton University in Boston. ?
Mac convinced J.T. that he really loved Brittany, but he wasn't able to tell her before Brittany married Bobby Marcino, so he reverted to his playboy past. Mac was able to get Kevin Fisher to open up to her, and convinced him to go to a psychiatrist. Kevin appeared to be learning how to deal with his past and handled it well when he realized that Mac was not interested in him as more than a friend.
J.T. had been assisting Paul Williams with his detective work on various cases while attending Genoa City University. Meanwhile, Mac and J.T. got closer, and she finally lost her virginity to him. But in an intricate plot to keep the mob away from Brittany and her unborn baby, they set it up to look like J.T. was the father, and Bobby and Brittany staged a split. For her safety, Mac wasn't included in the plot, and this "revelation" broke her heart.
Nikki started nosing around and uncovered the plot, and ended up getting kidnapped by Vinny's goon, Luca. Paul, Victor, and Bobby rescued Nikki, while J.T. took a distraught Brittany to the Newman Ranch. Luckily, Mac showed up as Brittany went into labor, and Mac delivered the two-month premature baby, Joshua. Vinny, Angelo, and his goon ended up in jail, Brittany and the baby in the hospital, and Bobby turned over his evidence on the mob and went into the witness protection program, leaving Brittany and Joshua behind.
J.T. confessed to Mac that it was all a hoax, that he really loved Mac, but she was reluctant to trust him again. Katherine Chancellor convinced J.T., Brittany, and her baby to come live at the Chancellor Estate with Mac, as it would be the most secure for all of them. Months went by, and finally Brittany shared a short visit with the heavily guarded Bobby. Not long afterward, she received word that a hit-and-run driver had killed Bobby.
Brittany was devastated, and she and Joshua ending up moving to New York City with her parents. Mac and J.T. moved into the loft apartment with roommates Kevin and Scott Grainger. Kevin became close friends with Mackenzie again, and they decided to go into business together. They convinced Nick and Sharon to sell Crimson Lights, and began running it together.
About the time Colleen returned to Genoa City intent on making Mac jealous, Mac discovered that she was pregnant with J.T.'s baby. She couldn't bring herself to tell him, but she told her grandmother Kay and Kevin. It wasn't until she miscarried that J.T. found out and was livid that she hadn't told him, yet confided in Kevin instead, so J.T. had a one-night stand with Victoria Newman.
Mac and J.T. broke up, and Mac moved out of the loft and back into the Chancellor Estate. She was getting closer with Kevin, then suddenly returned to the Indian reservation. Mac later returned to tell Kevin she was going to go to New Orleans to work with her father, Brock, and signed a power of attorney turning the coffee house over to Kevin. When Mac did not show up for her grandmother Katherine's funeral, Brock said she was ill and living in Darfur in the Sudan, Africa, following in his footsteps of helping out the needy.
In April of 2009, after Brock let her know that Katherine was alive, Mac showed up at the Chancellor mansion just in time for Billy's marriage to Chloe. Meanwhile in the next room, the results of Brock's blood test proved that he was Kay's son, and that Jill was not Katherine's daughter after all, which meant that Billy and Mac were not related either. Their reactions to the news made it quite obvious that both have never gotten over each other. After some persuasion by Murphy that Kay needed her, Mac decided to stay in Genoa City, which made Chloe concerned for her marriage.
Mac's old friend Kevin was committed for his own good after his arrest for bank robbery. Kevin became near-catatonic and delusional in a padded cell, and was okay with Mackenzie and Michael’s visits.
Mac's eighty year old grandmother, Katherine, married Patrick “Murph” Murphy in the Chancellor garden in a service officiated by her son Brock. Nikki was matron of honor, Victor best man (because Kevin was still locked up), Amber and Mac were bridesmaids. Ana sang “Let Met Call you Sweetheart”, and the catering was by Joe’s Diner, complete with chicken nuggets. Amber designed Kay’s white lace suit dress, and Nikki caught the bouquet. Michael got Kevin out on bail just in time to attend. Billy and Mac danced and shared how this wedding reminded them of their own long ago. Mac resisted Billy’s advances, and when he grabbed and kissed her, she slapped him. Chloe saw it, kissed his smarting cheek, and took him home.
Billy was upset when Cane bought his favorite escape, Jimmy’s Bar, but was elated when he hired Mac as a waitress, and began spending even more time there, avoiding Chloe. Billy keeps lamenting about their missed opportunity for happiness, and Mac keeps reminding him they have both moved on.
On Memorial Day 2009, Kay and Murphy threw a bar-b-q around the Chancellor pool with Esther, Billy, Chloe & Delia, Mac, Amber, Nina, and Jack in attendance. Later Sharon, Neil & Tyra, Kevin & Jana arrived. Raul Guittierez surprised everyone when he walked in. After reuniting with Billy and being introduced to Kay's new husband Murphy, Billy's new wife Chloe and their baby, Mac walked in and they embraced and passionately kissed. Mac had earlier revealed that there was someone she worked with in Darfur, Africa, and their year long relationship was "serious, but didn't work out" -- and it turned out to be Raul. After Billy reluctantly gave them his blessing, Raul asked Mac to marry him and return to Washington DC with him, and she said yes. But the more time Mac spent with Billy, the more she doubted her future with Raul. Chloe saw this coming and got Raul to return from DC, but it was only for Mac to tell him she was sorry, but the engagement was off. Billy and Mac were about to make love when Chloe interrupted with the news that the paternity test on Sharon's baby was about to come back. Mac did not take the news well that Billy might be the father of his brother's wife’s child, and left. But Mac realized this happened when they were not together, and after seeing Billy talking to God about saving Summer for him despite all his sins, she decided he was still the man she loved.
Sharon got the paternity test results back and was ecstatic that she and Nick are expecting the daughter Faith that Cassie predicted on her death bed and in Nick's dream. But after seeing Nick so distraught over his daughter Summer being in a coma, she realized that he needed to be there for Summer and Phyllis, and not run off with her like he did over Cassie, so she told everyone her baby was Jack's.
Billy and Mac faked being mad at each other at Kay’s 4th of July party, both made excuses and met at the Athletic Club to finally make love after all those years apart, but were interrupted by a phone call that Kay had another mini-stroke and was rushed to the hospital by ambulance.
Cane sold Jimmy's Bar to Mackenzie when he decided to leave town. But when Mac heard that Lily was in the hospital with ovarian cancer, and about to undergo surgery, she tracked down Cane, persuaded him not to leave town, and stashed him in Murphy's trailer home that Billy had just bought as a rendezvous for them. Whenever Mac and Billy met there, they had some intimate moments and memories, but always seemed to get interrupted by something, before they could finally make love after a six-year wait.
Victor called a press conference and named Mary Jane Benson as the person who hurt his grand daughter, so the entire city was looking for her. Mary Jane was discovered by Mac in an alley, and she befriended her thinking she was just a homeless person, giving her food, blankets and a place to stay in the back room at her bar. Meanwhile Jack and Paul banded together to find her themselves. After Victor asked for J.T.'s resignation, Paul talked J.T. into joining him in a new detective partnership, and he became involved in the Mary Jane Benson investigation. J.T. discovered through Mac that she had been hiding out at her bar, stolen from her and disappeared, leaving a note that claimed Victor knew all about Mary Jane.
After Mac admitted to Chloe that she and Billy were now together, Chloe got a divorce started, and Chance felt free to date Chloe. But when they met to sign the divorce papers, Billy started remembering the good times in the past, and backed out making excuses. So Chloe decided to use Chance to make Billy jealous and stay with her and Delia. Billy went back and signed the next day, but Chloe never did and they remained legally married, though separated. But after Chance was stabbed trying to stop a robber, Chloe realized how much she really cared and signed the divorce papers.
Mac wanted to help Lily and Cane by being a surrogate mother for them, but Billy refused to let her do it. Billy was not happy when Mackenzie volunteered and began looking into the legal ramifications with Michael Baldwin. Mac got a physical, and told Cane she was ready, even though Billy did not want her to do it. Mac and Billy broke up, and Mac became pregnant with Cane and Lily's child. Meanwhile Billy's life was spiraling downward again into drunkenness as he watched Chance take Billy‘s place with Chloe and his daughter, Delia, after losing the love of his life, Mac. Then an end-of-2009 visit from his dead father John, showing him what the future would be like with Billy dead if he kept this up, began to turn Billy around. He cleaned up the magazine’s reputation and mended fences with Jack and Mac, although Mac remained wary of him. But when it was time for Cane to be deported, she broke down and told Cane the truth, so of course he escaped. But just as he was apprehended, Michael saved the day with the news that he had arranged for Cane to stay legally because of Lily’s condition.
A sonogram confirmed that the twins Mac was carrying were boy and girl. Olivia approached Lily with an experimental procedure using stem cells from the babies’ placentas that could save her life, but both Lily and Mac turned it down fearing it may harm the babies. Instead Lily left for Europe with Olivia to try an experimental procedure, without Cane who would not be allowed back in if he left the country. Cane then decided to sue Mac for the right to take the placenta fluid against their wishes. A copy of Lily’s will arrived in the mail shortly after she left where she specified that in the event of Lily's death, she wanted Cane and Mac to have joint custody of the twins. Mac was not sure how to handle the news since she had been trying to distance herself from the babies she carried so as not to get too attached to them, and not so hard to give them up.
More and more, J.T. was left alone at home caring for Reed while Mackenzie grew larger pregnant with Cane and Lily’s twins, and she would often come by to help and they grew close again. Meanwhile Victoria was enjoying an affair with Billy Abbott. Victoria’s appeal for custody of Reed was lost because Tucker reported to the court that Victor kept J.T. from arriving in time. To top it off her divorce decree arrived later, so to get away and forget their problems, Victoria and Billy took the next plane to Kingston, Jamaica, with no luggage or plans. They joined a Jamaican wedding party on the beach where rum and Billy’s teasing and charm made him the life of the party. He made her laugh and smile again telling everyone about their love/hate relationship. Deliriously drunk, they got married too. Meanwhile, Mac, J.T., and Reed went for a drive in his GTO and ended up at a drive in movie watching The Three Stooges and eating nachos. They began to realize they had more in common now than ever, and the old spark was still there. As J.T. said, “The stuff you never see coming, is exactly what you want.”
After Lily’s procedure failed, she returned and took part in the hearing, but when Cane saw her emotions and frailty on the witness stand, he dropped the lawsuit. The next day, Mac went into early labor, the twins Charlie and Matilda (Matty), were born two months premature, and their amniotic fluid was saved for Lily’s treatment. Lily and the twins stayed in the hospital all growing stronger, as she got her treatments. Meanwhile Mac shared with J.T. her guilty regrets and missing the babies.
Lily was released from the hospital and welcomed home by the family who had unpacked all the baby gifts, and had their house all ready for them when they could come home. Cane and Lily visited the babies often, as deportation loomed closer for Cane once she got well. But Sofia saved the day by convincing Tucker to approve Cane as liaison with their corporate partner where Cane grew up in Canberra, Australia. Because Cane was uniquely qualified he obtained an eight month work visa. Cane and Lily eventually brought the twins home, and Lily’s health continued to improve. Lily asked Mac to be Godmother to the twins. When she turned her down explaining that she was getting too attached to them, Lily asked Traci, and she accepted in memory of Colleen. Devon felt honored to be the twin’s Godfather.
Kevin discovered that his wife Jana and half-brother Ryder had run off together and was afraid he would lose Crimson Lights without the bail money Jana had gotten for Ryder by mortgaging it. That came true when Ryder did not show up for his trial, but Mac came to Kevin’s rescue, offered to buy back Crimson Lights, let him run it, and split the profits 60/40.
Mac told J.T. that she wanted to return to Darfur to get her mind off the twins, but J.T. convinced her that her future was in Genoa City with him, and asked her to move in with him. Mac accepted, and Reed was thrilled. After Victoria learned that they were living together, she decided to fight for custody of Reed again. But J.T., pointing at the exposed “Billy Abbott” tattoo on her lower back, reminded her that with her lack of employment and a home, he would still appear to be the more stable parent and win.
Mac and J.T. decided to try to have a baby of their own, and it didn’t take long before Mac was pregnant. J.T. was offered a job as Civilian consultant to the Genoa City Police Department, and jumped at the chance to get away from the corporate world of the Newmans and Tucker.
In mid-October 2010, Cane, Lily, and the twins went to the lake in an attempt to escape Blake, the Australian who was watching them. Cane decided they should return to Genoa City when a policeman warned them that a tornado was headed their way. As Cane took their things to the car, he was jumped by Blake. They fought as the storm got worse, Cane overpowered Blake, and dragged him into a root cellar. Blake threatened Cane that if he turned him in to the police, Blake would expose the fact that Cane had been one of the cattle rustlers, but had turned on the gang to save himself. Blake offered to leave Cane and his family alone for five million dollars, which he was sure that Katherine and Jill could provide. Before leaving, Blake whacked Cane over the head with a pipe wrench.
While J.T., Mac, and Reed were having a family day, J.T. offered a ring and proposed to Mac. Mac was touched, said she loved him enough to marry him, but it had happened so fast and she liked things just as they were for now. As a storm approached, they stopped at the Athletic Club for dinner. J.T. received a call from a panicked Lily, who was hiding from a tornado under a table inside a cottage at the lake, telling him that Cane had disappeared. J.T. left Reed with Mac and drove up to the lake to help. J.T. left Reed with Mac and drove up to the lake to help. Cane made his way back to the cottage covered in blood and told Lily he never found the guy but had been hit by debris. Later, as Mac sang a lullaby to Reed, the tornado caught J.T. on the road and caused him to crash into a power pole. The pole and power lines fell on the car as J.T. climbed out into the rain, electrocuting him. Cane and Lily discovered J.T. unconscious in his wrecked car on the drive home. With no cell phone service, Lily went to a gas station they had just passed to call an ambulance. Cane removed the power lines from the car with a tree branch and pulled J.T. out, finding no heartbeat. J.T. had a “walking into the light” experience, but Cane brought him back with artificial resuscitation, and J.T. awoke gasping for breath.
Later at the hospital, Cane checked out fine and was uncomfortable when Lily called him a hero. Mac sat at J.T.’s bedside in intensive care, thinking him still unconscious, and poured her heart about how much she regretted acting so adult by not accepting his proposal. J.T. opened his eyes and said, “I knew you’d come around.” Mac notified Victoria that Reed was fine but J.T. had been electrocuted, so Billy drove Victoria to the hospital. Victoria told J.T. she remembered how he had sat vigil with her when she was in a coma, realized she almost lost him, and vowed they would get along. J.T. later asked Billy if he and Victoria would take care of Reed if he did not make it, and Billy assured J.T. that they would.
Meanwhile, Cane insisted that Lily and the twins move in with Neil so they would be safe, then Cane checked the Internet for how to take on a new identity, and found a dead person named James Collier who was born in 1973 like Cane.
J.T. recovered and his burns began to heal after several days in intensive care. Mac told J.T. that she wished he wouldn’t join the police force and that she had a better alternative for them both working in Washington, D.C. for a small non-profit that helped people in distress. But J.T. said that police work was his dream, his own way of helping people. Then J.T.’s doctor gave him the news that he had extensive heart damage due to the electrical current which would keep him from joining the force or doing anything else as strenuous or stressful.
Mac received a job offer from a non-profit in Washington, DC, and they decided it could be a new start for them both with J.T. working there too. J.T. and Mac packed to move, and J.T. gave Victoria the news that he intended to take their son Reed with them. Victoria threw a fit and J.T. reminded her that he had full custody. Victoria conferred with both Michael and Vance, who told her she had no right to stop them. Hearing the news, Katherine decided J.T. and Mac needed an impromptu wedding that very day. With the help of Chloe and Kevin, some strings pulled by Katherine to get a license, and Mac’s father Brock arriving to perform the ceremony, they were married at the Chancellor Estate. Paul was the best man, and Lily the matron of honor. Billy and Victoria attended the ceremony, ironically each extending their ex-husband and wife good wishes for a happy life together. Then after Victoria bade a tearful goodbye to her son, J.T., Mac, and Reed left for Washington DC driving the GTO off into the sunset.
Reed stayed with Victoria and Billy in Genoa City during the birth of J.T. and Mac's son, Dylan, but he returned to Washington D.C. afterward. Reed visits Victoria, mostly on holidays.
In August 2013, Mac received word that her grandmother, Katherine Chancellor had died. A celebration of her life was held September third, but Mackenzie sent her regrets, saying that she had personal issues to deal with. Days later when Katherine's will was read, Mackenzie, Phillip, Chance, Brock and Nina were bequeathed one quarter of her estate to be shared equally.