The former NSW Nationals leader has been blocked from starting the $500,000 a year post he created as trade minister until a parliamentary inquiry examines the circumstances of the appointment, with its first hearing on Wednesday.

That inquiry is separate to a review into the matter initiated this week by Premier Dominic Perrottet and headed by Department of Premier and Cabinet secretary Michael Coutts-Trotter.

The DPC review would reportedly allow Mr Perrottet to shut down the high-profile appointment, depending on what it reveals.

DPC on Saturday said Mr Coutts-Trotter had named former NSW Public Service Commissioner Graeme Head as an "independent expert" to conduct its review to ensure the "utmost independence and public confidence".

It said Mr Head, a partner at consulting firm EY Port Jackson Partners, would conduct the review for Mr Coutts-Trotter then report back to the department.

Prior to working in the private sector, it said Mr Head had a "distinguished" career in public administration and public policy including six years as NSW Public Service Commission boss, leading the NDIS Quality and Safeguards Commission, and holding leadership positions in NSW and federal government agencies.

The review would look at how the US trade role's employment arrangements were determined, the selection and recruitment process and if the process complied with the law, DPC said, adding it would be conducted immediately.

Mr Perrottet and senior government ministers have defended Mr Barilaro's appointment as the result of an independent process but Labor has said it doesn't pass the "sniff test".

NSW Labor leader Chris Minns on Saturday said unanswered questions remained about the international search for the role and the independence of the selection.

"We now know that there were changes to all of those things ... So we need this inquiry to take place," he said.

Australian Associated Press