Dr. Kevin Collins arrived in Port Charles on General Hospital in the early part of 1994. He came to town to help rehabilitate his identical twin brother, serial killer Ryan Chamberlain, who was in a mental hospital. Kevin felt that his brother was as much a victim as the women he killed and thought that he could help his brother get well with his own therapeutic methods. He had a hard time being accepted by the citizens of Port Charles because he looked identical to a man everyone feared and hated. Eventually, everyone came around, including Felicia Jones, who was terrorized by Ryan for almost two years. However, her fiancé, Mac Scorpio, was instantly suspicious and hostile to Kevin. Kevin visited his brother, Ryan, several times and thought he was making progress. However, he was unaware that Ryan was using him to escape the mental hospital.
One night, Kevin visited Ryan in his room alone. Ryan found out enough about Kevin to knock him out and impersonated him back in Port Charles. Kevin eventually managed to prove to authorities and hospital personnel that he was indeed Kevin and not Ryan. He raced to the church to stop Ryan from ruining Felicia's wedding to Mac. After that ordeal was over and Ryan was apprehended, Kevin saw him at the prison and confronted him. Kevin wiped his hands of Ryan again. However, Ryan wasn't through with Kevin. He managed to escape the prison and impersonate Kevin briefly in order to kidnap Felicia's baby at General Hospital. Kevin helped Mac and Felicia find Ryan and the baby in 1995. Ryan killed himself instead of being apprehended. Kevin still felt some guilt about Ryan's fate.
On a more romantic note, Kevin found himself befriending and counseling Lucy Coe. Lucy came to Kevin with a moral dilemma. He helped her as best as he could, but found himself attracted to her while at the same time as he was exasperated with her. They started dating soon after. They got closer when Kevin found himself haunted by the death of his former lover, Grace. Kevin confided in Lucy that Grace had drowned in a car he was in and that he was to blame for her death. Lucy helped him work through the past and got him to see a psychiatrist. Kevin went under hypnosis and came to the conclusion that Grace was driving the car when it went into the lake and that he was unconscious in the car and could not save her in time.
Lucy moved in with Kevin and they started a strong, loving relationship. However, Kevin couldn't continue moving forward until he dealt with his whole history. In 1995, he helped a young man named Stone Cates with dyslexia, and then helped him out emotionally when Stone was diagnosed with AIDS. Kevin was profoundly affected by Stone's eventual death. He also found himself becoming very close friends with his former foe Mac Scorpio. The two men buried the hatchet. They even dressed in drag to help expose a fraud named Madame Mia.
However, by 1996, things began to unravel for Kevin. He found himself having blackouts, where he couldn't account for certain times of the day. He also started acting erratically while teaching a psychology class at Port Charles University. Mac's niece, Robin, who was taking his class, noticed it and called him on it when he mistreated a student. Kevin started to lose more time he couldn't account for. He started stalking Felicia Jones like his brother Ryan had. He tricked her and kidnapped her. He held her captive at knifepoint at the summer home of his childhood, called Jasmine Island. Lucy found him and talked him into letting Felicia go.
Lucy convinced Kevin to tell her what happened to him and Ryan as children. It turned out that Kevin and Ryan's mother had been molesting Ryan, and Kevin found out when he was four years old by pretending to be his twin to see what his mother did with Ryan in the bathtub. Lucy stood by him after he was charged with kidnapping and stalking Felicia. Felicia was angry and pressed charges against him, but eventually dropped them when she realized he didn't intentionally try to hurt her. Kevin began treatment with Dr. Gail Baldwin and his medical license suspended.
While Kevin was unable to practice medicine, he wrote a fictional murder mystery novel called General Homicide. The novel was a bestseller and the characters were based on people who worked at General Hospital that he knew. However, the book caught the attention of a real psychotic killer. The killer started copying the style of the murders and killed several doctors and nurses at GH. Kevin enlisted the help of his friend Mac, the Police Commissioner, to help solve the murders. Kevin was stabbed when he got close to solving the crimes. The killer turned out to be Greg Cooper, a doctor who was kicked out of his internship because the Quartermaines gave the intern position to Karen Wexler after Greg was found to be unstable, according to his files.
When things returned to normal, Kevin proposed to Lucy and she accepted. Lucy was also thrilled to learn she was pregnant. However, tragedy struck when, several months in her pregnancy, she miscarried. The couple planned a double wedding with good friends Felicia and Mac but their wedding plans also took a different turn when Kevin learned that Lucy had lied to him about her indirect involvement in the car accident that left Lucy's surrogate daughter, Serena, blind. Kevin called off the wedding to Lucy. He was in for a shock, however, when he went to tell Lucy he wanted her back and found her in a Florida hotel room with Scott Baldwin. He was devastated and turned to his friend, Dr. Eve Lambert for comfort.
Kevin found himself falling for Eve and they started dating. They eventually fell in love, and got married. They were happy for a while, until a new doctor named Ian Thornhart came to town and got Eve's attention. Kevin didn't realize that Eve was falling for Ian because an explosion outside of a club was presumed to have killed Eve and Ian in a car. Kevin was devastated and leaned on Lucy for support. Kevin also had to deal with his past again, when Rachel Locke, the sister of his ex-lover Grace arrived in town. Rachel took a position at the hospital as a psychiatrist and tried to get revenge on Kevin by trying to ruin him. Kevin also was treating a young girl named Livvie. Kevin helped her through hypnosis and learned about her recurring nightmares where she was drowning. Kevin started to see parallels between Livvie's dreams and his past history with Grace.
With Lucy's interference, Kevin learned that Livvie's biological mother was Grace, not Rachel. Lucy used Kevin's hair as a sample for a DNA test to match with Livvie's hair sample. The DNA test proved that Kevin was Livvie's father. Kevin was happy with the news since he was growing quite fond of Livvie as her therapist and acknowledged they had always shared a deep connection. In the aftermath of the revelation of Livvie's biological parents, Rachel suffered a mental breakdown and ended up hospitalized in a mental institution and Livvie struggled to accept Kevin as her father. She eventually came to terms with the truth and allowed Kevin to be a part of her life as her father.
Kevin leaned on Lucy more as he adjusted to having a daughter and Lucy and Kevin became lovers again. Eve and Ian returned alive and well. Eve lost her memory for a time but eventually told Kevin she was in love with Ian. Kevin realized he still loved Lucy. He and Lucy got engaged again but dark forces, specifically vampire Caleb Morley, caused them to drift apart. Lucy learned she was a descendant of vampire slayers and was determined to rid the town vampires.
In time, Kevin realized Lucy's theories about Caleb's vampire status were correct and he joined Lucy in her crusade to protect the town. They believed they had banished Caleb but they were unaware he was still causing havoc. Specifically, Caleb planted doubts of Kevin's love and fidelity in Lucy's mind which drove her into the arms of Ian and she had a one-night stand. Despite Lucy's indiscretion with Ian, Kevin forgave her and he surprised Lucy with a wedding.
The transition to married life was not a smooth one as shortly after the wedding Kevin's friend Paige Smith arrived in town and moved into the lighthouse with Lucy and Kevin. Lucy was suspicious of Paige's intentions toward Kevin and he ended up in agreement with Lucy after Paige vanished when she was supposed to be caring for Lucy's adopted daughter Christina. Both Kevin and Lucy were shocked when they pieced together that Paige was actually an angel that had returned to earth to complete her unfinished business. The couple accompanied Paige to London and helped her realize she was related to the Barrington family. Paige vanished after she saved Alison Barrington's life. After Paige disappeared, he leaned on Lucy more than ever before when his former wife Eve was killed in a car accident.
Soon after Eve's death, Kevin was presumed dead. Lucy had encouraged Alison to pursue a candle making business, although Livvie had warned them that the candles were associated with witchcraft. Through a candle, Kevin made contact with the spirit of Rebecca Barrington and he vanished. Alison was charged with Kevin's murder, although Kevin was alive in Rebecca's world called Barnadoon. Lucy refused to believe that her "Doc" was gone and she was able to channel him via Ian. However, Lucy stopped her contact with Kevin once she realized the toll it took on Ian.
Lucy helped Rebecca's spirit rest by clearing her name and Kevin was free of Rebecca, but he remained trapped in the other world. He sent Lucy a message in the form of a dated portrait of her to restore her faith in him and their love. Lucy's cousin Rafe, an angel, intervened and lit a special candle that brought Kevin home to Lucy.
Once Kevin and Lucy were reunited, a wedge formed between them when they disagreed over which woman Rafe should be with. Lucy believed Rafe's true love was Alison, whereas Kevin took the side of his daughter Livvie and championed her cause. Kevin did agree with Lucy that his daughter was acting strangely and he decided to investigate. He found proof that Livvie had lied about the paternity of her unborn child to keep a hold over Rafe and planned to confront her. When he arrived at Livvie's apartment, she mistook him for someone else and injected him with a psychotropic drug. Kevin assumed the personality of his dead twin Ryan and seduced Lucy. Afterward he tried to kill her. He also tried to hurt Alison which prompted Lucy to have him committed to a psychiatric care center. It was also revealed that a young prostitute on Jasmine Island, the place where Kevin retreated to after being injected, was murdered.
In dealing with her pain, Lucy grew closer to Ian while Kevin seemed to get worse instead of better. Kevin was particularly agitated by the growing connection between his wife and Ian. It became increasingly clear that Kevin would not be returning to his normal self and Lucy moved on with Ian. In 2004, Kevin made an appearance on General Hospital when he returned to the Quartermaine home with Lucy to attend the memorial service for Lila Quartermaine.