Maggie Simmons lived on a farm out in the country where she had hired hands take care of her farm. Maggie was crippled as the result of a childhood auto accident which killed her parents. One day Mickey Horton, under the name Marty Hanson, stumbled into her farm house desperate for food and water, and collapsed. Maggie, who was lonesome for company, took Mickey in and cared for him in his weak condition.

Maggie and "Marty" continued to live on the farm, and in 1974 "Marty" and Maggie were married. Marty began reading about a treatment for injuries such as Maggie's being done at Salem University Hospital, and set up an appointment for Maggie to be checked out. However, when Maggie went to the hospital she saw on one of the desks she saw a picture of Mickey without a beard, and she heard stories about a patient named Mickey Horton who disappeared the time that "Marty" appeared at her farm. Maggie left the hospital and did not return or tell Marty what she learned. Later the Hortons would eventually be led to the farm after seeing Mickey's picture in a newspaper. Determined to stay married to Mickey, Maggie underwent the operation to regain the use of her legs in hopes it would help her hold onto Mickey.

In 1975 Maggie was operated on by Bill Horton, but she still could not walk. Laura Horton explained to her that her paralysis was no longer physical, but mental. Maggie was so afraid of losing Mickey that she was causing the paralysis in her mind. After Mickey divorced Laura, Mickey and Maggie were married on Jan 25, 1975.

Later, Linda Patterson would return to Salem with her daughter Melissa. Once she heard Mickey had no memory she tried to re-kindle her relationship with Mickey by convincing Mickey that Melissa was his child. However, Maggie had received a letter from Linda's husband warning her of Linda, and her plans were thwarted. Later (in 1976) when asked by Mickey if he could be Melissa's father Linda truthfully told him no, that Laura had told her he was sterile.

In 1976, Mickey was put into a Sanitarium after attempting to kill his brother Bill. Maggie stood by his side the whole time, and after spending a year in the sanitarium Mickey was released. Because Mickey and Maggie learned they would never have a child of their own because Mickey was sterile they adopted Janice Barnes.

In 1978, Janice was taken away from Mickey and Maggie by her natural mother Joanna Barnes. Janice was eventually found and returned to Mickey in Maggie, but Joanna took a job in Salem and stayed close to her daughter. This relationship took its toll on Maggie, who began to drink heavily. Later that year Maggie's drinking increased, and she was arrested when she had an accident with Janice in her car. Both were knocked unconscious and transported to the hospital.

Maggie joined alcoholics anonymous, but fell off the wagon when Janice's custody hearing grew close. When the possibility that Maggie may lose Janice to her natural mother Joanne, Maggie kidnapped Janice and fled town with her. She would eventually return to Salem after Tom Horton found her in a nearby town.

Later Janice would have an accident on the pier while playing with little Melissa. Janice fell into the water, and as a result slipped into a coma. Joanna Barnes and Maggie fought over her at the hospital, but in the end Joanna was given custody of her daughter.

In 1979 Maggie unknowingly sold some canes containing cocaine to costumers of Julie's shop. Later when a drug dealer came looking for them the two struggled and Maggie eventually shot him with his own gun.

In 1981 Maggie agreed to be a surrogate mother for an anonymous donor. Maggie went to Neil and agreed to be inseminated. Neil preformed the procedure, and Maggie soon became pregnant. Later that year Dr. Evan Whyland came to Salem and Neil knew he was the anonymous donor of Maggie's. When Evan learned about this he began to call on Maggie often.

Mickey learned that the baby she was carrying was Evan Whyland's, and even when he told Maggie she wanted to keep the baby, so Mickey agreed to love it as it was his daughter. In late 1981 Sarah Horton was born, and after a custody battle with Evan Whyland, Mickey and Maggie won custody of Sarah. Later Mickey and Maggie also got custody of Melissa Anderson.

In 1982 Evan often paid visits to Maggie and little Sarah, and Stefano suspected Maggie knew of Evan's evidence against him and tried to have Maggie killed by tampering with the breaks in her car.

Mickey and Don began to investigate Stefano after Evan Whyland had died, and when Mickey got to close to Stefano, Stefano kidnapped Mickey but made it appear that he had died in a car crash. Don began to spend time with Maggie, and eventually fell in love with her. When Don finally told Maggie she was speechless.

In 1983 Maggie and Don eventually professed their love to one another, unfortunately Mickey Horton had escaped from Stefano and returned to Salem. When he saw his wife and Don tell each other they loved the other Mickey had a heart attack.

Maggie and Mickey divorced in 1983, and soon after Maggie stopped seeing Don, realizing her divorce from Mickey was a mistake. Mickey was accidentally shot during a gang rumble, and he recuperated at Maggie's house, and the two re-kindled their love. On February 14, 1986 Mickey and Maggie remarried in a double wedding with Melissa Anderson and Pete Jannings.

Maggie and Mickey's marriage was in trouble by 1990. Mickey was always at work and constantly let down Maggie and missed dinner dates and other important functions. Maggie ended up seeking solace in the arms of Dr. Neil Curtis. Maggie's daughter, Sarah, caught Maggie and Neil and took pictures of them together in bed. Sarah was ready to expose them when Maggie and Neil revealed a shocking secret to her, Neil was Sarah's true father. Sarah still exposed them and the news devastated her adopted father, Mickey. Though Mickey was hurt, he felt he was partly to blame for Maggie's infidelity. Mickey and Maggie patched up their marriage and Dr. Neil Curtis left Salem.

When Julie Williams left Salem in 1993, Alice and Maggie Horton turned Wings into Alice's restaurant.

In 1993, Alice and Maggie Horton invested in Billie Reeds up and coming cosmetics company Countess Wilhelmina. Maggie had very little story after that, until she purchased Tuscany, and made herself into the town busybody.

In 2003, Mickey and Maggie were attacked in their home. Mickey survived, but unfortunately, the hit from the alcohol bottle and a deep stab wound ended Maggie's life. She was the third victim of the serial killer.

Maggie returned to Salem in 2004 when she and the rest of the serial killer "victims" were rescued from the island where Andre had kept them. Maggie's return was bittersweet as she learned that Mickey had moved on with his life and married Bonnie Lockhart. Desperate to win her husband back, Maggie, Doug, and Julie worked hard to show that Bonnie was just trying to extort money from Mickey and that she never really loved him. They were successful and Mickey and Maggie settled back into their life together. Maggie began running the upscale restaurant Chez Rouge and Mickey continued to practice law. Maggie continues to be the primary confidant and supporter of her nephew-in-law Lucas.

In the summer of 2008, Maggie made a push to turn Chez Rouge into an environmentally friendly "green" restaurant. Maggie swapped out appliances, table linens, and other materials to make Chez Rouge the first five star restaurant to be certified "green" in Salem.

In the fall of 2008 Maggie needed to be there for another nephew, Nick Fallon. Nick became addicted to pain pills and started terrorizing Salem's newest residence- Trent Robbins and Melanie Layton. Maggie fought hard to get Nick the help he needs to break his pill addiction and rehabilitate his mental state. She even agreed to give Melanie Layton a place to live after Nick was arrested to help Melanie get back on her feet after the attack. Maggie formed a bond with Melanie and frequently offered the 18 year-old life and love advice.

Throughout 2009 Maggie and Mickey continued to look after Melanie and grew to love her like their own child. Eventually, they opened their hearts and home again when they took in troubled teen Mia McCormick and temporarily housed Dr. Nathan Horton, their grandson by Melissa. Nathan eventually moved in with Lucas, but not before Maggie gave him his great-grandfather Tom Horton's medical bag – a treasured family heirloom and a testament as to how proud she was that he was following in Tom's footsteps. With her grandson in Salem, Maggie's life was in a good place, despite the (welcomed) stress of mothering two teenage girls with chaotic love lives.

By the winter of 2009/2010, Maggie's life was as busy as ever. In addition to running Chez Rouge, she continued to volunteer at the hospital and host AA meetings. Mickey was equally as busy with his bustling law firm. Unfortunately, because of their full lives, they barely saw each other and it was starting to strain their marriage. Enter Doug and Julie. They had just returned from a cruise around the world and encouraged Maggie to convince Mickey to go on one, too. As luck would have it, he agreed to go. They both cleared their schedules and prepared for a long voyage of rest, relaxation, and togetherness. However, a blindsiding tragedy would prevent Maggie and Mickey from setting sail.

In mid-January 2010, Maggie went upstairs to help Mickey finish packing for their trip and found Mickey dead. Her attempts at CPR were too late. He had died of natural causes. Family and friends gathered in Salem to mourn Mickey's passing, celebrate his life, and support Maggie who was devastated by his death. However, being the constant rock for everyone, Maggie refused to be fussed over and tried to carry on with her life.

While mourning, Maggie contemplated taking a drink after a box of Mickey's belongings arrived from his office. In the box was a bottle of whiskey that a client had given him and he kept at the office out of respect for Maggie. Despite being upset after finding a heartfelt anniversary gift he never had the chance to give her amongst the box's contents, Maggie stayed strong and poured the alcohol down the drain. Instead of drinking, she decided to focus on the positive and even encouraged Melanie to go through with her wedding despite her recent loss. It was a bittersweet moment when Melanie married Philip Kiriakis on Valentine's Day, which was also her anniversary with Mickey.

When Melanie was shot at her wedding, Maggie stayed at her side throughout her recovery. However, Maggie would soon have her own medical problems to worry about. She began to have dizzy spells and even fainted on a few occasions. Dr. Daniel Jonas noticed this and convinced her to seek help as they both feared her myasthenia gravis, a rare muscle disease, was returning. Despite being newlyweds, Philip and Melanie decided to temporarily move in with Maggie and look after her.

Their presence also meant that Victor stopped by Maggie's house to visit Philip. As Maggie and Victor spent more time together, Maggie realized that she was developing feelings for Victor. The two began spending more time together, and continued even after Melanie and Philip moved out.

Maggie's relationship with Victor made her very happy, but also put her in danger. Victor's wife, Vivian, was not happy about Victor's friendship with Maggie. So, Vivian hatched a plan to burry Maggie alive. Brady, Victor, and the rest of Salem wondered what happened to Maggie. Victor finally figured out where Maggie was and rescued her. But as the story came out that Victor had had a hand in keeping Vivian prisoner, Vivian was able to blackmail Brady to keep him from revealing her plot to the police. Maggie was upset, but eventually found that she couldn't stay away from Victor.

Soon, a war between the Kiriakises and the DiMeras broke out. When Maggie feared that Victor would be the target of an assassination attempt, she went to warn him. Unfortunately, Maggie ran right into the path of the bullet and suffered serious injuries. Frightened that the war had gotten to such a level, the Kiriakis and DiMera families called a truce. Maggie went home to Victor's house to recovery.

As soon as she regained her strength, Maggie made plans to move out. Victor asked her to stay, but Maggie said that she wouldn't live with a man unless they were married. A few weeks later, at the opening of the Horton Town Square, Victor proposed. Maggie was thrilled to accept his proposal. They were married in November 2011.

Victor wasn't the only new man in Maggie's life. Bo and Hope found documentation at Alice's house, leading to the revelation that Maggie's eggs were used by another woman to conceive a child. The investigation led Maggie to learn that a woman named Lillian Parker had used Maggie's eggs, making Daniel Maggie's biological son. Maggie worked hard to form a relationship with her new son, and continue the already blooming relationship with her granddaughter, Melanie.

With her personal life in great shape, Maggie set out to expand her professional life. In May 2012, she purchased the Intensity Day Spa.