The Police Ombudsman's Office was established in November 2000 to provide independent, impartial investigations of police complaints in Northern Ireland. Prior to the founding of the Police Ombudsman, police complaints were investigated by other police officers under the direction of the Independent Commission for Police Complaints for Northern Ireland.

In 1995, during peace process negotiations, Dr Maurice Hayes, a senior civil servant and chairman of Community Relations Council was asked to review existing police complaints procedures in Northern Ireland and make proposals for a new system that would be acceptable to all communities and to the police force. In 1997, the “A New Police Ombudsman for Northern Ireland?” report was published. The report found that the existing police complaints system was inadequate and recommended that a Police Ombudsman Office be established with a team of independent investigators tasked with dealing with complaints against the police. The Hayes report was supported by all political parties and the RUC and the Police (Northern Ireland) Act 1998 established the role and powers of the new office. The Independent Commission on Policing in Northern Ireland agreed with the findings and proposals in the report stating that the Police Ombudsman Office was “critical to the question of police accountability to the law, to public trust in the police and to the protection of human rights.”

The Police Ombudsman's Office investigates current and historic cases and deals with a wide range of complaints from alleged use of rude language by officers to failure to conduct proper inquiries. The Current Investigations Directorate deals with complaints about incidents that have occurred within the previous year. The Historical Investigation Directorate was established in 2010 to investigate the conduct of the RUC during the Troubles.