Josh Murray will on Thursday be the first in a string of public servants to appear at an upper house probe, investigating the circumstances of his recruitment.
Transport Minister Jo Haylen has come under heavy fire in recent days for appointing Mr Murray, who critics say was an outside candidate for the $588,000-a-year job.
Most recently she was forced to defend a combined $750 donation by Mr Murray and his wife to her political campaign, which she did not formally declare until after he was given the job.
Ms Haylen will not face the inquiry, her office confirmed.
"It's parliamentary convention that neither lower house MPs nor ministers appear in upper house inquiries, with the exception of budget estimates," a spokesman for the minister told AAP.
Ms Haylen's chief of staff, Scott Gartrell will appear at the inquiry, along with acting secretary of the premier's department, Peter Duncan.
Former Labor minister Verity Firth, who sat on the transport secretary recruitment panel that recommended Mr Murray, will also be called.
Mr Murray, a former executive at global engineering and construction company Laing O'Rourke, and chief of staff to former Labor premier Morris Iemma, began his tenure two weeks ago as questions were raised over his appointment.
Documents provided to parliament show recruiters aired concerns about his experience but later interviewed him at the suggestion of Ms Haylen's staff.
Opposition transport spokeswoman Natalie Ward said MPs wanted to understand the process for hiring Mr Murray, who she says went from being under-qualified and a risk in the eyes of recruiters to "being catapulted into a half-million dollar job".
Premier Chris Minns has defended Mr Murray and Ms Haylen and denied the ministerial code of conduct had been breached.
The inquiry beginning Thursday will also examine the COVID-time appointment of Nationals federal secretary Emma Watts as NSW cross-border assistant commissioner.
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