NIB chief executive Mark Fitzgibbon will retire from the company on November 30.
Mr Fitzgibbon, who turns 65 in November, was also the health insurance company's managing director.
He joined NIB in 2002 in both roles, which he held for more than two decades.
Mr Fitzgibbon led NIB's demutualisation and listing on the ASX in 2007. NIB is now an ASX100 company.
The health insurer's board announced Mr Fitzgibbon's retirement date on Thursday, saying Ed Close would take over the two roles on December 1.
Mr Close is currently chief executive of NIB's core Australian Residents Health Insurance business.
When his pending retirement was first revealed in July, Mr Fitzgibbon told the Australian Financial Review that he wanted to "get his golf handicap down".
He also wanted to finish a book about leadership lessons.
Last month, NIB announced a net profit of $181.6 million.
Total revenue increased to $3.3 billion, up by 9.3 per cent on the previous financial year.
NIB's annual report said its Australian health insurance membership increased by 18,000 people, or 2.5 per cent, to almost 715,000 policyholders.
Mr Fitzgibbon linked the rise to long wait times in public hospitals.
"It underscores a very serious inconvenient truth - that the public health system is struggling to cope," he said last month.
"We have an ageing society and limited tax dollars.
"As a society, we need to come to grips with the reality that the public medical system can't pay for everybody."
He added that the number of people who had taken out private health insurance had "increased every quarter for the past 15 quarters".
"Thankfully the pandemic is behind us, yet its consequences continue to play out," he said.
"People are today more aware of risks to their health and the need for protection.
"Extreme pressures on the public healthcare system makes private health insurance all the more attractive to consumers."
NIB announced in March that it would increase health insurance premiums by an average of 4.1 per cent.
This was above the insurance premium average of 3.03 per cent.
The company said it factored in rising inflation, after two historically low rises.
Amid premium rises across the sector, private hospitals have been under financial pressure.
The private hospitals have criticised private health insurers - which have recorded rising members and profits - for not paying enough to the hospitals.
The federal health department is reviewing the private hospital sector's financial viability.
