Corbett was born John McGillis in Belfast, Northern Ireland on June 3rd 1979 to Anthony McGillis and Anne Marie McGillis. His parents died in 1984 and 1989, resulting in him being adopted in 1990 by his aunt Sorcha Corbett, and her husband Robert Corbett. After his adoption he subsequently moved to Liverpool where his adoptive parents lived.
He married Stephanie Miller in 2009 and the two had two young daughters, one of which is named Gemma. Despite working in the The City in the West Midlands, it appears he and his family live on the outskirts of Liverpool.
Prior to joining the police, Corbett worked in the printing industry. He became a police officer in March 1999, undergoing training at the Bruche Training Centre, where he also obtained certification as an Authorised Firearms Officer and took an Advanced Driving Course. He first worked for Merseyside Police, but later joined Central Police after becoming involved in Operation Pear Tree. Certificates of commendation in his home indicate for a time he may have also worked for the East Midlands Constabulary.
After passing training, he was assigned to Beeston Station in 2000 and then Viewlaine Station in 2002. After passing the detectives course in 2001 he was stationed with Vice Squad out of Menton Station. He later took both parts of the OSPRE exam in 2006 and 2007, and was issued a commendation for outstanding bravery in 2008. After becoming Detective Sergeant in 2009 he was stationed at Dockton Station in 2010, and received another award for outstanding bravery the same year. From 2010 to 2014 he underwent specialist undercover training.
In 2015 he was assigned to the Serious and Organised Crime unit in Salvesen Road Station. He was recruited by Detective Superintendent Alison Powell as part of Operation Pear Tree, where he was planted undercover in the Organised Crime Syndicate under the name John Clayton, a criminal forger. However, he quickly broke off contact with his handlers and began committing serious crimes beyond his permitted remit.
Along with Lisa McQueen, Ryan Pilkington, Miroslav and Lee Banks, Corbett leads the hijacking of police transport ED-905, which is transporting heroin for incineration from the Eastfield Police Storage Facility. He and the men gun down three Authorised Firearms Officer's: PC Ray Randhawa, PC Kevin Greysham and PC Carl Waldhouse, and leave their leader Sergeant Jane Cafferty badly injured. Corbett prevents Ryan Pilkington from shooting the convoy's fleeing civilian driver, believing he will be unable to make the shot with an Uzi submachine gun.
After hijacking the truck and taking it to a disused barn in the countryside outside The City, Corbett congratulates his men and tells them to start moving the drugs. At the groups offices in the back of Kingsgate Printing Services, Corbett is confronted by Lisa McQueen whilst he is drinking with Miroslav, who confesses she lied about Sergeant Jane Cafferty dying in the ambush. Corbett angrily responds that the living officer will be able to ID McQueen, and informs her she will need to make up for her mistake.
Corbett and the group later meet with Paul Slater, the leader of a biker gang that serves as a rival to the Organised Crime Syndicate, and the people who originally owned the heroin before it was confiscated by Central Police. Corbett coldly informs Slater they are willing to return some of the merchandise, but expect to be allowed to keep half (of either the drugs or their street value) due to the resources they invested in retrieving it, and that they are not scared of entering into conflict with the gang if they do not agree to their terms (noting they were willing to kill three Authorised Firearms Officer's during the attack). Slater appears to reluctantly give in to Corbetts proposition, and the group returns to another of their fronts, Flicker nightclub. Corbett celebrates by taking cocaine and spending the night with two prostitutes, dismissing McQueens concerns about being double crossed by Slaters gang.
At Flicker the following evening, he informs Lisa McQueen they are ready to proceed with the exchange of the heroin with Slater's gang, but demands that she lead the exchange in his place to prove she is up to the job after lying to him about Sergeant Jane Cafferty. McQueen is able to secure the deal with Slater, but is told by Corbett during celebrations she needs to further inform a man named Vihaan Malhotra of consequences should he talk to Central Police about his role in the hijack.
Corbett and the group find themselves in luck when they are approached by PC Maneet Bindra, who agrees to help them in exchange for them not further injuring her cousin Vihaan Malhotra whilst he is incarcerated in HMP Blackthorn for his role in the ED-905 hijack. She makes an anonymous call, and Corbett has his men place a van full of heroin outside of Paul Slater's hideout. Slater and his gang are later arrested by members of the Strategic Firearms Command and Serious and Organised Crime Unit, putting them out of the picture and allowing the Organised Crime Syndicate to operate with even less competition in The City.
Meeting with Lisa McQueen, Corbett voices his concerns about the legitimacy of PC Maneet Bindra agreeing to work for them. He has Lee Banks and Ryan Pilkington kidnap her and bring her to the groups hideout at Kingsgate Printing Services, where he accuses her of still being loyal to AC-12, and using helping her cousin Vihaan Malhotra as a convenient excuse. Examining her burner phone, he discovers it has been bugged. Furious, he tells McQueen (who provided the burner) to get out of his sight, saying he will "deal with her later". He then orders Pilkington and Lee to kill Bindra, which they do at the same location the bodies of Oliver Stephens-Lloyd and ACC Derek Hilton were found.
Superintendent Ted Hastings threatens to issue Detective Superintendent Alison Powell with a Regulation 15 Notice unless she reveals the identity of her undercover officer who has been committing crimes. She reluctantly reveals that Corbett is actually a Detective Sergeant with the Serious and Organised Crime Unit, who was embedded into the Organised Crime Syndicate as part of the highly secretive Operation Pear Tree. However, she indicates he has gone rogue, and has not been in contact with her or his handlers for multiple months. Corbett is shown looking concerned, sipping a glass of whiskey in Flicker.
At Kingsgate Printing Services, Corbett is seen managing a group of Asian migrant workers constructing fake British passports. He is confronted by Lisa McQueen about disposing of PC Maneet Bindra's body at the quayside, as it has attracted police attention. Ignoring her concerns, he states that since the group has suceeded in obtaining the heroin and putting Paul Slater's gang out of business, they could do with some more support from "above" (meaning H). McQueen warns him for not following orders, especially since she has been and "earned" her place in the Organised Crime Syndicate for longer than him. He retorts by claiming they are both in the business for the same reasons: money, power and respect.
When AC-12 officers DI Kate Fleming and DS Steve Arnott visit Corbetts home to speak to his wife, Steph Corbett, various commendations are seen on the walls showing that when he was a Detective Constable Corbett appeared to have worked or liaised with the East Midlands Constabulary, as well as police forces in the South of England. His wife appears less than concerned that he has dropped off the grid, accusing him of infidelity whilst he has been placed undercover.
After Ryan Pilkington and Miroslav are able to identify and prevent DS Steve Arnott from receiving a burnerphone after he attempts to contact the Organised Crime Syndicate the same way PC Maneet Bindra and Vihaan Malhotra did, Corbett congratulates them. He then inquires as to whether Arnott is corrupt, to which Miroslav and Pilkington deny given their previous involvement in torturing him during the blackmail of DCI Tony Gates in Series 1. After Lisa McQueen obtains information from Sergeant Jane Cafferty about a second police convoy, Corbett also congratulates her.
Along with Ryan Pilkington, Miroslav, Lee Banks and other members of the Organised Crime Syndicate, Corbett orchestrates and takes part in a second police convoy attack and hijacking. Information on the convoy, which is transporting confiscated automatic weapons from the Midlands Forensic Ballistics Laboratory for destruction, was provided to the group by Cafferty. During the hijack, Corbett gives his men specific instructions not to kill the Authorised Firearms Officer's providing security, but to simply pin them down and trap them in their vehicles by shooting the armoured plating. When Lee Banks attempts to shoot one officer who emerges from a car, Corbett prevents him from doing so. After the hijack, Banks and Lisa McQueen put him in contact with "H", who admonishes him for committing an unauthorised hijacking. He responds by claiming that with the weapons they stole they are well armed enough to raid and rob the Eastfield Police Storage Facility, and could steal all the seized contraband instead of smaller amounts from transports. H considers the idea, but then disconnects the call.
Corbett kidnaps DS Steve Arnott from the basement carpark of his home at Kingsgate Apartments, and handcuffs him in the back of a car which he proceeds to drive away. Speaking with Arnott, Corbett claims he is both innocent and not corrupt, and has been doing everything he has to get higher up in the Organised Crime Syndicate to uncover the identity of its police leader. He voices his vapid disdain for corrupt officers, claiming he only killed PC's Ray Randhawa, Kevin Greysham and Carl Waldhouse during the ED-905 ambush because they were corrupt, and argues that it was PC Maneet Bindra's action that got her killed, not him directly. Corbett goes on to inform Arnott be believes he has made contact with "H" via computer link, but needs to obtain the computer from a safe controlled by Lisa McQueen if they stand any chance of tracing him. He criticises senior police leadership for covering up the extent of police corruption, claiming DSU Alison Powell and Operation Pear Tree drifted the mission focus away from him identifying corrupt officers. He also voices his suspicion about Superintendent Ted Hastings, who he notes could have brought in Robert Denmoor for questioning instead of shooting him, and was not punished by the Chief Constable for doing so. He urges Arnott to work with him, before returning him home and leaving.
After Lee Banks is arrested by Strategic Firearms Command when he attempts to deliver a pay off to Sergeant Jane Cafferty, Corbett instructs Miroslav to look into other members of the group, claiming they have a rat. This causes him to be confronted by Lisa McQueen, who sincerely tells him to be careful using that word, and tells him how Tommy Hunter, the former leader of the group, was killed whilst in witness protection for snitching to Central Police. That evening he meets again with DS Steve Arnott, where he argues he has proved himself by providing information that led to Banks and Cafferty's arrests. Corbett claims he is doing more than anyone else to try and uncover corrupt officers, accusing Arnott for being partially culpable for Maneets death after he and DI Kate Fleming backed Superintendent Ted Hastings after her dismissal, and that to avenge her death Arnott should help him. He later uses a burner phone to contact Steph Corbett, where he apologises for not calling more often and asks to hear their two young daughters sleep. The two appear to be very much in love, with Corbett having told Steph to lie to AC-12 about their relationship beign fractured.
At Kingsgate Printing Services, Corbett outlines his plan to rob the Eastfield Police Storage Facility to other members of the group. He notes that although they have large amounts of firepower from the stolen weapons from the Midlands Forensic Ballistics Laboratory, it is safer to get in quietly. For this, he instructs Lisa McQueen to use her contacts with corrupt officers in Central Police to help reduce the potential response to the robbery, as well as paying off the driver and security guards at the facility.
McQueen puts him in contact with H, who agrees to the raid due to the high value of the seized good stored in the facility. Afterwards, he asks Lisa McQueen as to the identity of the mysterious ringleader, to which she replies she doesn't know, and is glad for her own sake. Later that evening Corbett meets in secret with DS Steve Arnott, where he provides him with McQueens identity and burner phone number, on the contingency it is only used for surveillance purposes. Back at Kingsgate Printing Services, he is informed by Miroslav that a lorry has been acquired for the job, and that the security guards at the site have been paid off. During the meeting he receives a call from Arnott, who informs him that AC-12 is due to conduct raids on both Pulton House (one of the gangs brothels) and the print shop. Corbett diverts suspicion by telling the others he is speaking with a keen woman he has been seeing.
That evening Corbett confronts Arnott again in the basement carpark of Kingsgate Apartments, where he admonishes him for allowing the raids of the two properties to be conducted. He accuses Arnott of being like DSU Alison Powell and ignoring the extent of corruption within Central Police, which Arnott refutes. Despite the animosity, Corbett informs him of the OCG's plan to rob the Eastfield Police Storage Facility, and there is a strong likelihood a senior corrupt officer will be present. Back at Flicker, he is quizzed by McQueen as to how he knew how to clear the group out of Kingsgate Printing Services before it was raided, to which he responds it was simply luck, and it is basic common sense to move around whilst planning a large job.
On the night of the raid, he angrily confronts Lisa McQueen when the senior officer she promised does not turn up to meet them before they head to Eastfield Police Storage Facility. Deciding to continue, Corbett accompanies McQueen, Ryan Pilkington, Miroslav and various other members of the Organised Crime Syndicate to the depot, where they are let in by the bribed guards and take control of Warehouse 2 in the facility. During the robbery, Corbett uses a police radio to listen into the fake Status Zero call by PC Kieran Bloom, but despite the concern of police heading their way orders the group to continue packing.
Much to his surprise, the senior officer McQueen promised (later revealed to be DCS Lester Hargreaves) arrives at the facility, and aids the group is disabling tracking devices placed on the evidence. However, as the officer prepares to leave, Corbett becomes enraged and shoots him multiple times in the legs with an M4 assault rifle. The group leaves the facility, with a car carrying Corbett, Miroslav and Ryan Pilkington at the back of the convoy. They are pursued by DS Steve Arnott and officers from the Strategic Firearms Command down a disused service road, however Corbett is able to disable the cars engine by shooting it.
Meeting later with DS Steve Arnott, he accuses the detective of betraying him by not being present to arrest DCS Lester Hargreaves when he arrived at the facility. When Arnott angrily informs Corbett that Hargreaves is dead, he seems genuinely surprised, claiming he shot Hargreaves in the legs with only the intent of immobilising him so he would be unable to escape AC-12. He angrily chasitises Arnott for leaving the scene to attend the diversion created by PC Kieran Bloom, and once again accuses Superintendent Ted Hastings of being H due to his actions on the night of the Eastfield raid. Arnott becomes tired of Corbett's "bullshit" and moves in to arrest him, but Corbett pulls a pistol and fires a warning shot to keep him at bay. Tearfully, he admits he didnt intend to kill Hargreaves, and admit's he has now crossed the line. Realising he is now on his own outside of Central Police with no way back, he declares he will now try and complete his mission by his own rules.
After fleeing Arnott, Corbett turns up at the apartment of Roisin Hastings, using a counterfeit Central Police Identification Card and claiming he is Arnott, and needs to speak with her regarding a sensitive matter. When Roisin asks him to wait whilst she contacts her husband, Corbett dons gloves and a balaclava and forces his way into the apartment, shutting the door behind him.
It is revealed that after gaining access to the apartment, Corbett tortured Roisin Hastings into revealing information about her and Ted Hastings private life and finances, including the fact they are in considerable debt due to investment in The Kettle Bell Complex. During the torture Corbett affected a Northern Irish accent and used methods similar to paramilitary groups in the region, leading AC-12 to believe he may have a connection with the area.
In the basement of Flicker, he and Lisa McQueen communicate with H via the encrypted laptop, who reveals that despite the robbery netting a large potential profit, the goods have become too hot to move due to the high profile nature of the operation. In an argument with McQueen, he insists that H is likely a corrupt officer in Central Police. He later attempts to meet DS Steve Arnott in the basement parking garage of Kingsgate Apartments, but backs off when he notices additional security cameras and a police patrol. Instead speaking with Arnott on the phone, he reveals audio footage of him torturing Roisin Hastings, and further insinuates Superintendent Ted Hastings is corrupt due to his considerable debt.
Accompanied by Lisa McQueen, Ryan Pilkington and Miroslav, Corbett arranges a meeting with another rival gang run by Khan to attempt to move the goods stolen from the Eastfield Police Storage Facility. Khan's group refuses, as the stolen goods are still too hot, but propose that they instead provide a location for the OCG to run their brothels, as despite still having "supply lines" of women their main brothel location at Pulton House is now under the control of Central Police after being raided. Corbett dislikes the attitude of the rival gang and attempts to make his group leave, but McQueen overrules him and strikes a deal with them. After making the deal, he argues with McQueen over the nature of the "livestock trade", insinuating it is too risky. McQueen conveys her personal dislike of forcing women into sexual slavery, but retorts that it is simply business and needs to be done. She informs him that she has arranged a face to face meeting with H.
Corbett calls Stephanie Corbett to let her know he is alright, and she informs him that DI Kate Fleming and DS Steve Arnott visited her again, and were asking questions about his connection with Northern Ireland. She asks him as to whether Central Police know about Anne Marie McGillis, to which he responds he cannot talk about his work. By monitoring the communications of his wife AC-12 are able to track Corbett to an apartment development in Verona Walk in the Kingsgate area of the city. He is confronted by DS Steve Arnott, who is being monitored and watched by Superintendent Ted Hastings, DI Kate Fleming and a Strategic Firearms Command team led by Sgt Kyle Ferringham from a distance. Although surprised to see Arnott, he tells him that Lisa McQueen has arranged a face to face meeting with H, and is he is arrested now they will be unable to bring down the majority of the Organised Crime Syndicate. During their argument, Corbett admits to torturing Roisin Hastings, which enrages Hastings who orders Arnott to bring Corbett in. The two eventually pull weapons and enter into an an armed standoff, causing Hastings to issue a Fahrenheit shoot-to-kill order. Corbett questions whether Arnott cares more about justice or orders, causing Arnott to disconnect his wire. Upon doing so, Corbett reveals the meeting with H is due to take place at the Palisades Shopping Centre that afternoon . He is then able to escape from Sgt Kyle Ferringham's SFC team via a hidden exit route.
Corbett accompanies Miroslav and Lisa McQueen to the Palisades Shopping Centre to meet with H, however they leave when he is a no show. During their time at the centre they are under observation from AC-12 and members of the Strategic Firearms Command, however operationally cannot be arrested due to the firearms risk to the public. Later that evening at Flicker, he is informed by McQueen they have been contacted again by H. However, this is in fact Amanda Yao and members of Central Police Cyber Crime, who were able to gain enough data from the raid at Kingsgate Printing Services to mimic the communication. During the text and speech conversation, Superintendent Ted Hastings takes over from Yao, telling the group they need to get the goods stolen from Eastfield Police Storage Facility out of the country.
Corbett meets later that evening with Miroslav and Lisa McQueen, who are in the process of bringing a group of Eastern European women to a building owned by Khan's gang under the auspice they are a legitimate employment agency. However, once inside the women are violently manhandled by the gang and Ryan Pilkington, and taken to separate rooms to be "processed". This appears to disturb both Corbett and McQueen. With McQueen implying she has had enough and wants to leave the Organised Crime Syndicate due to the nature of their "business" with trafficked women, he and John appear to form an alliance.
Later in the building, Miroslav and other members play poker whilst the noise of the crying women is heard in the background as they are processed. Ryan Pilkington later leaves to "control" them, with it sounding like and being implied he is raping one of the women. Infuriated, John picks up a pistol owned by Miroslav and holds the group back whilst he and McQueen make their way to the room where Ryan is to free the women. However, upon opening the door he discovers another member of the gang simulating sex noises, which distracts him long enough for Ryan Pilkington to sneak behind him and slit his throat. As he bleeds out on the floor he is surrounded by Ryan, Miroslav and McQueen, who tells him she had figured out he was a rat. Corbett fruitlessly fires one round from the pistol before finally bleeding out and being dragged away by Miroslav.
In evidence obtained by DI Kate Fleming and DS Steve Arnott, it is revealed that prior to being recruited into Central Police to take part in Operation Pear Tree, Corbett was approached in secret by Gill Biggeloe. Having researched into his past, Biggeloe was able to manipulate and convince Corbett that it was Superintendent Ted Hastings who was responsible for the death of his mother Anne Marie McGillis in Belfast decades prior. She presented him taking part in Operation Pear Tree as an effective way of seeking revenge on his mothers killer, and later pulled strings with DSU Alison Powell and PCC Rohan Sindwhani to ensure Corbett was selected from the operation.
DI Steve Arnott visits Lee Banks in prison to question on him on his contact with Gail Vella prior to hi death. At the end Lee Banks claims that it was Ted Hastings who told him that there was an undercover officer inside the Organised Crime Group, blowing Corbett's cover leading to his death.
During a search of the White Rock Industrial Park, a metal strongbox is discovered under the concrete floor. Among other items, it contains a knife stained with the blood of Corbett with fingerprints matching Ryan Pilkington on the handle. The finding seemingly confirms to AC-12 that is was Pilkington who murdered Corbett. This finding would seem to contradict the testimony of Lisa McQueen who claimed it was Miroslav Minkowicz who was responsible for Corbett's death. Testimony in exchange for which she would receive immunity from prosecution.
Ted Hastings confesses to Steve Arnott and Kate Fleming that he did indeed disclose to Lee Banks that there was an undercover officer inside the Organised Crime Group. However, Hastings insists that he did not tell Banks that Corbett specifically was an undercover officer, only that an undercover officer was among their ranks. Hastings claims his intention was to scare Corbett handing himself in for protection, not to set in motion events that would lead to his murder. He also notes that Corbett has been responsible for the murder of four police officers, and had tortured his wife.
Despite this, Hastings acknowledges that he knew there was a risk of Corbett coming to harm, and expresses remorse for his actions. Hastings states that "if there was one thing I could take back [from his career in policing], it would be that". He says that Stephanie Corbett is still unaware of any role he may have played in her husbands death, but that giving her £50,000 of OCG bribe money was by way of atonement.