|Title||Chief of Operations|
|Precinct||One Police Plaza|
|First Appearance||"The Blue Wall"|
Peter "Pete" O'Farrell is Captain Cragen's former mentor and former Chief of Operations (now known as Chief of Department).
During his time as a cop, Chief William Wilson acted as O'Farrell's mentor and handpicked O'Farrell to succeed him as chief after he retired to run for Congress. For the next 20 years, O'Farrell acted as Donald Cragen's rabbi during his time on the police force. He handed Cragen every of his promotions, even personally handing him his Captain's shield. When Cragen's precinct, the 2-7, investigated and arrested three Colombian drug dealers and their three bankers, Congressman Wilson contacted O'Farrell.
Wilson asked O'Farrell to help him erase the contents of two computer disks implicating the bankers because they contributed enormous amounts of money to his campaign. The bankers offered Wilson $300,000 to do this, which Wilson was willing to split with O'Farrell and he accepted. To this end, he had Wilson bribe O'Farrell's old driver, Officer Albert McCrory, who was retired, with Wilson's wife's old house to take care of it. After Wilson bribed McCrory, O'Farrell told McCrory to approach Detective Dennis Shearer, who worked in Computer Forensics, the day after he got the disks and gave him $20,000 to give him the disks. After McCrory erased the disks, he gave them back to Shearer and slipped them back into the property clerk's office.
The Blue Wall
When the three bankers are acquitted, the Manhattan District Attorney's Office launches an investigation into how the evidence against them was erased, O'Farrell being one of the targets. He later has lunch with Sergeant Greevey and Detective Logan. After tells them a story he tells them the reason Schiff is targeting him and Cragen is to find some Irish cop scapegoats. He then goes on to say that they were probably the ones who messed up the disks. When McCrory's involvement is discovered, O'Farrell, Willson and McCrory are arrested and arraigned with all three pleading not guilty and released on $50,000 each.
Detective Shearer accepts a plea after his involvement is discovered and testifies against all three. Although the proof a crime was committed was established, the defense team manages cast reasonable doubt on O'Farrell and Wilson's involvement. O'Farrell later attends a police ceremony with Cragen and the two talk about the case. When Cragen says he's scared of being indicted O'Farrell sets his mind at ease that McCrory is a good cop and he didn't do anything for Wilson, unaware that Cragen is wearing a wire.
When O'Farrell hears Cragen is being indicted, he invites Cragen over for a drink and tells him not to worry. Cragen tells him that he was some of his detectives' memos implicating O'Farrell and that he will burn them to protect O'Farrell. O'Farrell was so happy Cragen was loyal to him and offered him a third of the $300,000 and confessed everything to him. He was shocked, however, when Cragen testified against him in court about everything O'Farrell told him and attempting to bribe him. O'Farrell, Wilson and McCrory are convicted of bribe receiving in the second degree, conspiracy in the third degree and tampering with physical evidence.