Kiwibank chief executive Paul Brock is stepping down after seven years in the role and more than 17 with the company.
Brock has been with the bank since it was launched in 2002 and was appointed chief executive in 2010.
Since it was founded, Kiwibank has grown its customer base to more than a million.
Bank chair Susan Macken commended Brock on having led it through a period of rapid growth.
She said the board and shareholders thanked him for his contribution in making the bank such a success.
In the last year there have been major changes to the bank including New Zealand Post selling 47 per cent of its shareholding - 25 per cent to the New Zealand Super Fund, and 22 per cent to ACC.
Brock said his 17 years in the business had been "very rewarding" but he would be taking a break to consider what the future held.
Kiwibank would look for a replacement chief executive immediately.