Westpac chief financial officer Peter King will retire in 2020 after 25 years with the bank.
The company says Mr King has given 12 months' notice and will continue in his role until a successor is appointed following an international search.
Mr King has been CFO since 2014, before which he was deputy CFO.
He said the bank had transformed into a more customer-focused organisation during his tenure.
"While we have more work to do, I believe Westpac is on the right track to not only continue to be financially successful but to be an organisation that customers want to bank with, and staff are proud to work for," Mr King said in a statement.