Traditionally the office had been very small, but was expanded from 2014 onwards in response to controversies over unlawful activities to include a Deputy Inspector-General, two external advisors, and a number of investigation staff.

[2] That expansion was accompanied by some greater resourcing and a more intensive role, in particular with the addition of an own motion power of inquiry, and quickly resulted in a significantly larger number and depth of inquiries, including into systemic issues and matters of public controversy such as an incident involving adverse allegations arising from briefings claimed to have been given by the Security Intelligence Service to the Leader of the Opposition [3] and the conduct of the agencies in parts of the conflict in Afghanistan.

[4] Senior political figures have at times criticised the extent of the broadened independent oversight that followed the 2014 reforms.

The IGIS is an independent oversight body, with a broad function of assisting the Minister responsible for NZSIS and GCSB to ensure the activities of each agency comply with the law; ensure that complaints relating to these agencies are independently investigated;[7] and review those bodies' compliance procedures and systems.

The Inspector-General conducts inquiries into matters of concern, including individual complaints, and reports consequent findings and recommendations to the Minister.