The Public Sector Investigations Unit came into existence in July 1997 when the WA Police Service was restructured. Its predecessor was the Official Corruption Unit, established in 1985, as a squad of the Criminal Investigation Branch.

The squad contributed significantly to the investigative capacity of the Royal Commissions into Commercial and Other Activities of Government, City of Wanneroo, and Use of Executive Powers. The squad followed up on issues arising from the activities of those Commissions but not directly related to their Terms of Reference.