In 1965, Mickey started a relationship with Diane Hunter, whose divorce case Mickey was dealing with, and helped her to deal with her daughter Susan. Diane and her husband later got back together, mainly because of Susan, but in 1966, Laura Spencer arrived in Salem. Bill later set the two up and after the David Martin murder case they grew closer and became engaged. They married the next year. Mickey later tested to see if he was unable to have children but the results were forgotten about when he discovered that Laura was pregnant, however the father of this unborn child was not Mickey. Little did he know that his brother, Bill Horton had raped Laura in a drunken rage. When Tom saw the results of Mickey's test, he confronted Laura who lied and said that she had given in and slept with Bill. They agreed to keep quiet to protect the family. In November 1968, Michael william Horton was born and Mickey still had no clue.

Mickey later had an affair with his secretary, Linda Patterson, in 1970. After Mickey refused to leave Laura for her, Linda attempted suicide and broadcast her affair to the whole of Salem. However, Mickey and Laura stayed together for the sake of young Michael. When Michael learned of the affair, in 1973, he confronted Mickey, who suffered a heart attack. His brother, Dr. Bill Horton, performed a life saving operation which pulled Mickey through. However shortly after, Mickey suffered a stroke but managed to walk out of the hospital. However, he was left with amnesia and had forgotten a lot, including his name. Mickey invented a new name for himself: Marty Hanson, he walked out of Salem and was taken in by a crippled farm girl called Maggie Simmons they soon fell in love and married in January 1974. Mickey later saw operations being offered at Salem University Hospital for Maggie's disabilities. Later, after his picture appeared in the paper, Mickey was reunited with the Hortons, though he had no memory of them. Bill offered to operate on Mickey in hopes of returning his memory, but Mickey refused.

After Bill's operation on Maggie fails, Mickey pointed the finger at Bill for her inability to walk, although Laura told Mickey and Maggie the paralysis was mental now. Mickey promised Maggie she would walk again and her took her back home to her farm. Mickey then divorced Laura who had been having an affair with his brother, Bill. Then he and Maggie married in October 1974.

In 1976, Mickey learned that he was not Mike's biological father. After Mike suffered an accident on Maggie's farm, Mickey and Laura donated blood. When neither matched, Mickey realized he could not be Mike's father. Mickey looked through medical records, and when he found out his brother Bill was a match, all of Mickey's memory came back to him. Mickey then went to Linda Patterson and asked if Melissa could possibly be his child, and she told him no because he was unable to have children, according to Laura Horton. Angry at being lied to for years Mickey bought a gun and plotted to kill Bill, and when the two fought over the gun it went off, shooting Bill in the arm. After the fight, Mickey suffered a mental breakdown and was admitted to Bayview Sanitarium for a year. After Mickey was released, he and Maggie adopted Janice Barnes. In 1978, Janice was taken from Mickey and Maggie by her mother Joanna Barnes. Janice was found and went back to Mickey and Maggie, but Joanna accepted a job in Salem and stayed near her daughter. This relationship took its toll on Maggie, who began to drink heavily. Eventually Mickey and Maggie lost custody of Janice to her mother in 1979.

Clarke is the longest-tenured original Days of our Lives actor after onscreen mother Frances Reid (Alice Horton), appearing in the role for 39 years. He was nominated for a Daytime Emmy Award in 1979 for Lead Actor in a Drama Series for his portrayal of Mickey.

Mickey Horton got a bad rep for never winning a case. He defended Salemnites for decades, many of his clients have ended up in jail for crimes they didn't commit. In the table, unless otherwise noted, Mickey represented the defendant. He spent a few years as assistant district attorney in the late 1980s.

Mickey found out that the baby she was carrying was Evan Whyland's, and even when he confronted Maggie with the facts, Maggie stated that she still wanted to keep the baby no matter who the father was, so Mickey agreed to love it as it were his own child. In late 1981, baby Sarah Horton was born, and following a custody battle with Evan Whyland, Mickey and Maggie finally won custody of Sarah. Later Mickey and Maggie also got custody of Melissa Anderson who had run away from boarding school after the death of her adoptive sister, Mary. Linda had come back for the funeral, and attempted to remove Melissa from the Horton household, which made Mickey and Maggie decide to fight for custody of Melissa. Linda did not show up for the custody hearing, and the judge granted them permanent custody.

Mickey was kidnapped by Stefano DiMera after Mickey discovered that Stefano was blackmailing Evan and that Stefano was the mastermind behind Maggie's car accident. In 1983, Mickey escaped the DiMera island and arrived back in Salem to find that Maggie, believing Mickey was dead, was now having a relationship with Don Craig. The revelation gave Mickey a second heart attack, from which he eventually recovered. Maggie and Mickey divorced that year but Maggie soon realized that she was still in love with Mickey. Maggie left Salem for New York in the fall of 1984 after Linda Anderson had returned to make amends to her daughter, Melissa, but was really after Melissa's shares of Anderson. Her scheme failed, and Linda left Salem for good in late 1985, right after Maggie had returned from her year's sabbatical. Mickey was shot in a gang rumble and recovered at Maggie's house. Mickey and Maggie remarried in 1986.

In 1988 Mickey ran for a seat in the Senate, and his rival was none other than Jack Deveraux. Jack was going out with Mickey's adoptive daughter Melissa, and even proposed to her. However, Melissa learned Jack was using her, and got rid of him.

Maggie and Mickey's marriage had hit rock bottom by 1990. Mickey was always at work and always disappointed Maggie and missed romantic meals with her. Maggie ended up in the arms of Neil Curtis. Maggie's daughter, Sarah, caught Maggie and Neil in the act and took photos of them together in bed for evidence. Sarah was ready to tell Mickey and reveal their secret, when Maggie and Neil revealed that Neil was Sarah's true father. Sarah still exposed them and the news destroyed Mickey. Though Mickey was frustrated and greatly hurt, he felt he was the reason for Maggie's affair. Mickey and Maggie repaired their marriage and Neil left Salem.

Mickey was usually seen whenever a Salem character had legal problems and needed an attorney. In 2003, Mickey was absolutely heart broken when he and Maggie were attacked in their home by the Salem Stalker; Mickey got stabbed with a scalpel but unfortunately Maggie was killed due to a blow to the head from a wine bottle. A few months onward, a confused Mickey was eventually released from his sorrow by Bonnie Lockhart, whom he married soon after, not before learning Maggie had not really died but her death had been faked and she had been kidnapped and trapped by the DiMeras, like the other Salem Stalker victims, in a plot to get rid of Salem's best-loved residents. Mickey was torn, because although Maggie was back, he was legally married to Bonnie since his marriage to Maggie was deemed invalid by her apparent death. After months of going back and forth between the two women, Mickey finally picked his original love, Maggie.

Over the past years, Mickey has been in Chicago covering several trials and has been rarely seen in Salem. On December 23, 2008 Mickey spent time with his mother Alice watching classic Christmas films at the Horton house. Mickey returns to Salem again on December 24, 2009, for the Horton Family Christmas sitting in the kitchen with Alice. On December 31, 2009, Mickey is unable to return to spend New Year's Eve in Salem and calls Maggie to let her know. During their conversation, Maggie and Mickey decided to spend more time in the new year. They plan to go on a cruise because Doug and Julie always tell them how beautiful they are. Maggie reflects on the great times she has shared with Mickey over the years. On January 5, 2010 Maggie tells Bo that Mickey will be returning home so they can go on a New Year's cruise.

Mickey died from a heart attack while packing to go on a cruise with Maggie on January 8, 2010. Maggie found Mickey's body and came downstairs in shock. Hope came while Maggie was still in shock and noticed something was wrong, she went up stairs to check and called 911. The paramedic removed Mickey's body from the house. On January 14, 2010, the Hortons celebrated Mickey's life with a memorial Service that brought together the entire family. His life and the love of his life, Maggie, were celebrated. His daughter, Melissa, returned to comfort her mother during this difficult time. In June, Mickey's mother, Alice Horton, died of natural causes. Maggie and Julie celebrated Alice's relationship with her son, Mickey.