Since its establishment the Office was solely responsible for investigating complaints against Government Ministries and Crown Agencies under the Ombudsman Act 1984. In February 2008, this increased to include the Official Information Act 2008. This gave the Ombudsman the mandate to investigate and review complaints about decisions made by Ministries, Ministers of the Crown and Crown Agencies on requests for official information held by the Cook Islands Government.

The Disability Act 2008 gave the Ombudsman the role of investigating complaints where people living with a disability or their agent, feel that they have been discriminated against on the basis of their disability.

In 2012, the jurisdiction of the Ombudsman was further increased to include the Police Act 2012. This empowered the Ombudsman to investigate complaints in terms of the conduct of police officers, issues relating to policies and procedures. The role of the Ombudsman is the equivalent of the role of the New Zealand Independent Police Conduct Authority.