NIB chief executive Mark Fitzgibbon says he will retire from the company on September 1.
Mr Fitzgibbon 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.
He led NIB's demutualisation and listing on the ASX in 2007. NIB is now an ASX100 company.
NIB group chair David Gordon said Mr Fitzgibbon had been "a tremendous leader", who had an "enormous impact on the Australian health sector".
NIB began in 1952 and now provides more than 1.6 million Australian and New Zealand residents with private health insurance.
Its members include about 200,000 international students and workers, along with 40,000 in Australia's disability sector.
It is Australia's third-largest travel insurer.
Mr Gordon said Ed Close had been selected as NIB's incoming managing director and chief executive.
He is presently chief executive of NIB's Australian Residents Health Insurance business.
Mr Fitzgibbon said he was "very pleased for Ed".
"He is an outstanding leader and will continue to be supported by NIB's world-class executive team," he said.
"I look forward to working with him during the transition period."
NIB said Mr Fitzgibbon wouldn't be doing interviews ahead of the company's full year earnings result - to be announced on August 26.
However, he joked to the Australian Financial Review's Chanticleer section that he was retiring because "I didn't want to do a Joe Biden".
Mr Fitzgibbon, who turns 65 in November, added that he wanted to "get his golf handicap down" and finish a book about leadership lessons.
He told the Newcastle Herald last year that the rising movement of healthcare consumerism was equivalent to the rise of streaming TV services in the Netflix age.
"Netflix is bringing entertainment into homes in a way we couldn't imagine not that long ago," Mr Fitzgibbon said.
"It's also personalising the experience, serving up content which its algorithms predict will be of most relevance and interest to you."
The healthcare sector was adopting this model, with products and services - including apps - that boost patient awareness of their health and the benefits of preventing disease.
"Within a generation we've seen an emergence of healthcare products and services that are different to the traditional system of doctors, dentists and hospitals," he said.
In March, NIB announced an increase to its health insurance premiums by an average of 4.1 per cent, which was above the insurance premium average of 3.03 per cent.
Mr Ftizgibbon's retirement announcement followed news earlier this month that NIB members may not be able to use their hospital cover for surgery at St Vincent's hospitals.
Contract negotiations with St Vincent's Health fell apart, after the two parties worked for months over a new contract.
St Vincent's said it intended to walk away from the deal, claiming the offer from NIB didn't come close to covering the cost of providing hospital services.
The private hospital sector has been under financial pressure for years, with operators saying benefits paid by private health insurers are too low.
