Born in 1942, Marie is the youngest of Tom and Alice's children. She grew up in the Horton House with her siblings, twins, Tommy Jr. and Addie, as well as Mickey and Bill. She would eventually become a biochemistry graduate student at Salem University.

In 1964, Marie became engaged to the affluent Rick Butler. However, their engagement didn't last and, by 1965, she was engaged to her neighbor, Tony Merritt. Although Marie was happy, Addie found her sister's choice of husbands a poor one as Rick had been wealthy whereas Tony was "merely" a teacher. The sisters bickered over the issue several times, but, never the less, Marie and Tony planned a Thanksgiving wedding and to move to Boston shortly after. Tragically, Tony suddenly called off their engagement the night before their nuptials, causing Marie to fall into a deep depression.

After Marie attempted suicide, it was Tony's father Craig who helped her through the dark times. They fell in love and married in 1966. Marie soon became pregnant with Craig's child, but, unfortunately, suffered a miscarriage causing her to fall into yet another depression. This one was worse and Marie began hallucinating, often hearing the sounds of babies crying. Craig thought he could help Marie through it as he did before, but, around this time, he found out why his son had called off his marriage to Marie. Tony thought he was dying of a rare blood disease and didn't want Marie to watch him die, but had since fully recovered. When it became clear that Tony and Marie still loved one another, and their reuniting would help Marie, Craig divorced her and left Salem to allow them to be together.

Throughout 1967, Marie tried to work things out with Tony. However, she had grown from her eye-opening life experiences and was not the same woman as before. She also found it hard to trust Tony again and ended their relationship. Tony left Salem later that year and Marie returned to her job as a lab technician at the hospital.

In late 1967, Dr. Mark Brooks joined the staff at Salem University Hospital. Marie became his research assistant, but soon fell in love with him. He fell for her too, but didn't rush their budding romance which would ultimately turn out for the best.

In 1968, an explosive reveal rocked the Horton family. Mark was revealed to be Tommy Horton, Jr., who had not died during the Korean War. In truth, he was captured by the enemy and severely tortured in 1953. Tommy would later escape and have plastic surgery to repair his face which had been severely scarred, but he remained amnesic. Using the name of one of his friends, he eventually gravitated toward Salem and the Horton family. Marie was utterly devastated and horrified that she had fallen in love with her own brother. By the end of the year, she ran off to Africa to become a medical missionary and, after some time in New York City, she eventually became a nun hoping that, by serving God, her sins would be forgiven.

Sister Marie returned to Salem in 1970 to support her family when Bill was accused of murdering Kitty Horton, Tommy's wife. She stayed to see her family through the hard times and others that followed. However, she eventually left town again.

In 1979, Sister Marie returned home once more. While in Salem, she came face to face with Alex Marshall and it stirred up feelings she thought were far behind her. Marie had known Alex and his brother Haley when she spent time in New York during the years she was out of Salem. While in New York, Marie and Alex had a fling and she became pregnant. However, when she joined the convent, she was forced to give up her child after it was born. When Marie was called back to her convent later that year she was delighted, and she prepared to leave Salem.

However, Marie left the convent in 1980 and returned to Salem to locate her long lost child, Angelique Horton. At first, she searched Canadian hospital records, but she came up empty handed. Marie eventually discovered her daughter under the name Jessica Blake, though she never revealed to Jessica that she was her mother. Marie found out that Alex had become found of the young girl, and the two quarreled over her, but she never revealed to him that she was his daughter.

In 1981 Alex legally adopted Jessica and, soon afterwards, Marie told him the truth about their daughter, but made him promise not to tell her. He agreed to Marie's wishes. Alex also wanted to re-kindle their romance, but she refused to break her vows. Later, Alex and Marie went on a trip to Canada to learn more about Jessica, but on the way their plane crashed. The two were forced to spend the night in a nearby cabin, and re-kindled their relationship.

Later that year Alex eventually told Jessica that he was her father. She accepted him, but hated Marie for giving her up and keeping Alex from knowing the truth. Marie and Jessica had many heated confrontations over the issue. Yet despite Jessica's feelings, Alex and Marie planned to marry once Marie officially left the convent. Marie visited Montreal and formally resigned, but their wedding was delayed when Jessica ran off to join a convent. When Marie would eventually straighten things out with Jessica, Mary Anderson would pose a new threat to her relationship with Alex.

Mary still wanted Alex back, so she tried every trick in the book to make Marie think Alex was having an affair with her, and Marie eventually fell for it. Marie left him, and shortly after Alex was shot. He fell into a coma and, when he woke, he discovered he was paralyzed from the waist down and had no memory of who shot him. Marie moved back in with Alex to take care of him, but would not sleep with, or marry, him just yet.

During this time, Jessica had developed multiple personalities (Jessica, Angel, and Angelique) and started causing problems for Marie, Alex, and others in Salem. When Marie's niece Hope finally discovered the truth, she told her aunt, who was devastated over her daughter's condition. Marie immediately flew to Las Vegas and was able to stop Angel (Jessica) from marrying Jake Kositchek, who would turn out to be the infamous serial killer, the "Salem Strangler." Jessica had a mental meltdown and Marie was there to help her daughter throughout her long recovery process, although Marie and Alex eventually parted ways in 1982.

In late 1982, Marie comforted Dr. Neil Curtis, who was rejected by Liz Chandler. They soon began to date and, several months later, married in 1983. However, Liz hated Marie for marrying Neil, and Marie hated Liz because she knew Neil still loved her. The two fought bitterly over Neil. One day Liz snuck into their apartment and slept with Neil. Later that day, after Neil was called to the hospital on an emergency, Marie returned home. Liz thought Marie was a burglar and shot Marie. Marie recovered, but Liz was sentenced to five years in jail. After her recovery Marie divorced Neil.

After two more, less eventful, years in Salem, Marie left town again in 1985. She returned in 1994 for her father's funeral and has since made occasional visits. One of her most recent was in January 2010 when she returned for Mickey's funeral, however she remained off-screen.

Marie returned to Salem once again in June of 2010. This time she ventured home to say goodbye to her mother who was slowly slipping away. Marie was reunited with her brother, Bill, as well as several other family members. They shared good memories of Alice as well as baked her famous doughnuts. Sadly, Alice passed away on June 23, 2010.