The resignation comes amid allegations from Australia's financial crimes regulator AUSTRAC that Westpac had breached anti-money laundering and counter-terrorism financing rules more than 23 million times and had failed to monitor transactions that may have involved child exploitation.
AUSTRAC said in a statement of claim that Westpac had engaged in widespread, systemic and frequent failures to adhere to laws combating money laundering and terrorism financing.
Chairman Lindsay Maxsted said the board accepted the gravity of the issues raised by AUSTRAC.
"As was appropriate, we sought feedback from all stakeholders including shareholders and having done so it became clear that Board and management changes were in the best interest of the bank."
In New Zealand, the Reserve Bank has said that it was working closely with its offshore regulatory counterparts on the matter.
Westpac said its current chief operating officer, Gary Thursby, will step in as chief financial officer.
In addition, long-standing director, Ewen Crouch had decided he will not seek re-election at next month's annual meeting.
Maxsted also confirmed he will bring forward his retirement as chairman to the first half of 2020.
He said the board accepted the gravity of the issues raised by AUSTRAC.
"We are determined to urgently fix these issues and lift our standards to ensure our
anti-money laundering and other financial crime prevention processes are industry
leading," he said.
On the NZX, Westpac's dual-listed shares have dropped by $2.34 or 8.3 per cent to $25.81 since AUSTRAC's allegations first came to light last week.
