National Australia Bank boss Cameron Clyne will retire in August, to be replaced by Bank of New Zealand boss Andrew Thorburn.

Mr Clyne, 46, on Thursday said that while leading the bank had been the most rewarding role of his career, the job had taken a personal toll and it was time to retire from executive life.

“I am leaving to spend some much-needed time with my young family,” he said.

“I am proud that I leave NAB as a strong, customer-focused bank.”

Mr Thorburn will take the reins of NAB, one of Australia’s big four banks, from August 1.

He has headed Bank of New Zealand, which is wholly owned by NAB, since 2008 and was previously NAB’s head of retail banking.

NAB shares were down 12 cents, or 0.34 per cent, at 1010 AEDT on Thursday.

Morningstar analyst David Ellis said the departure of Mr Clyne, who has led NAB since 2009, had caught the market by surprise.

“It was certainly a surprise to me and I’m sure it would be a surprise to most of the market,” Mr Ellis said.

He said while NAB had dragged behind its main competitors Commonwealth Bank, ANZ, and Westpac in recent years, it was unlikely Mr Clyne had been forced out.

“I believe him when he says he wants to spend more time with his family,” he said.

“Obviously that is often code for something else, but I think in this case he has done a good job in the five years he’s been in the role.”

Mr Clyne had managed to “right the ship” after inheriting a string of problems following the global financial crisis (GFC), particularly with NAB’s British subsidiary Clydesdale Bank, Mr Ellis said.

“He was appointed right in the midst of the GFC, it was a very trying time, and I think he’s done a very good job.”

NAB chairman Michael Chaney said Mr Clyne had led significant cultural and structural change during his time as chief executive.

“He is highly regarded throughout the bank and externally, and we are sorry to see him leave at this time, he said in a statement,” he said.

His replacement, Mr Thorburn, will take over on August 1.

AAP