NAB, parent group of BNZ, confirmed McEwan's appointment in a statement this morning.
Kiwi McEwan joins in November, after resigning from UK bank Royal Bank of Scotland in April this year.
The veteran banker previously held roles at CBA, where he was executive general manager, managing the bank's branch network, contact centres and intermediary relationships.
McEwan has a long career in financial services including several years at insurance provider National Mutual. He became CEO of the Australian firm in 1996, before its takeover by French giant Axa three years later.
At NAB, McEwan will replace Philip Chronican, who will replace Ken Henry as the bank's chairman.
McEwan's hire comes after a tumultuous period at troubled British bank Royal Bank of Scotland. RBS, partly-government owned and one of the biggest European casualties of the GFC, was forced to slash its branch network and staff numbers to return to profit. However, the bank's share price fell under McEwan's leadership.
His appointment comes at a difficult time for NAB, which was hammered by the Royal Commission for conduct and culture failings. The Commission led to the resignation of CEO Andrew Thorburn and chairman Ken Henry.
"It is a privilege to return to Australia and lead NAB at a crucial time for the bank, its customers, employees, shareholders and the broader community," Mr McEwan said.
"There are a number of areas where NAB can extend its lead, such as business banking, agriculture and health, and other areas where I believe we should consistently lead such as customer service. We must also meet and exceed the expectations of our many stakeholders.
"It is essential that I protect and accelerate the bank's transformation program. The community also expects a higher level of accountability and transparency from the banking industry. Australians deserve NAB to be a world class service provider," McEwan added.