He was portrayed by Corbin Bernsen from 2004 to 2006.
In 2004, Carly hired Coleman Ratcliffe to help her find her biological father. She had always thought that her father was one of her mother Bobbie Spencer's johns from when she was a prostitute. But when Carly found her mother's diary from when she was a teenager, Bobbie talked about a guy her age that she had a relationship with; she only listed him as "JD" in the diary.
Carly figured that this person could be her father. Coleman eventually tracked down John Durant in New York City, and a DNA test proved that he was a "close genetic relative" to Carly. Bobbie wasn't positive that John was her father since she had been a prostitute and it could have been any one of numerous guys she didn't know, but she did confirm that she had a relationship with John.
John became suspicious when Carly approached him, and suddenly left. He found out who she was, and followed her back to Port Charles, wanting to get to know his daughter. Carly and John struck up a relationship. There was one problem though: John was a prosecuting attorney who targeted organized crime. He went after mobster Sonny Corinthos, Carly's husband. After meeting Carly, he decided to use their connection to bring Sonny down, with assistance from his colleague, Dr. Steven Webber. Sonny and his enforcer Jason Morgan were both onto John, and warned Carly to stay away. Carly refused, and wanted to get to know her father.
As John got closer to Carly and his two grandsons, Michael and Morgan, he started to waver on his resolve to bring down Sonny. Carly divorced Sonny, and John bought her a house to move into with her sons. While moving, John happened to find a file with Sonny's dirty business dealings that got mixed up with Michael's items while they were packing. He took the file, and anonymously left it to be found by the District Attorney Ric Lansing. Sonny and Jason figured it out, though, and tried to get the file back. Carly set fire to Ric's apartment in an attempt to destroy it. When she was questioned, John provided her with a fake alibi. However, Carly later found out what John had done, and confronted him, saying she does not want him near her or her family.
John confessed to the police that he had illegally obtained the file, choosing his daughter over his career. Soon after, he took over as District Attorney of Port Charles. When Michael, Morgan, and Sonny's daughter Kristina Davis were kidnapped, John saw an opportunity to convict Sonny when FBI Agent Reese Marshall was assigned to investigate the kidnapping. Reese refused, and John held off, wanting to find his grandsons. Morgan and Kristina were found, but Michael was presumed dead. Sonny retaliated by killing the Sandoval mob family he believed was responsible. John got Reese to investigate, and implicate Sonny in the murders. She couldn't find evidence, so John blackmailed Maria Sanchez into giving a false witness statement by threatening to arrest her son, Diego. Reese figured it out, though, and chose to drop the case. She and Ric got evidence that proved John was corrupt, and John was forced to cooperate.
Michael was actually alive and was recued, but the kidnapper, A.J. Quartermaine, died at the hospital, and it was determined he was murdered. John found out that Sonny, Carly, and Jason believed Michael was responsible, and tried to keep him from confessing. John hoped to use this as leverage to convict Sonny and Jason, and bribed Michael's therapist Dr. Asher Thomas. However, this backfired when Dr. Thomas was revealed to be the killer.
Carly started dating and later maried Lorenzo Alcazar, an arms dealer who John also tried to prosecute. Carly was torn between supporting her father and defending Sonny and Lorenzo.
John was shot and killed in 2006 while he and Carly were caught in a gun shootout with mobster Manny Ruiz.