Sir John Key has been named chairman of ANZ Bank's local arm.

Key joins the board of the country's biggest bank from today and will assume chair at the start of next year.

It is the second corporate board the former PM has joined and follows his appointment as an Air New Zealand director.

Existing ANZ chair John Judge will retire from January.

David Gonski, who chairs ANZ Group's operation in New Zealand, Australia and elsewhere, paid tribute to Judge.

"John Judge's tenure has overseen significant change in the ANZ New Zealand business," Gonski said.

"The National Bank and ANZ brands and technology systems were successfully merged in 2012 and the business has grown significantly. ANZ New Zealand now has the biggest market share for home loans, deposits, credit cards and KiwiSaver, and is leading the way with digital services."

Gonski welcomed Key.

"Sir John Key's strong international career in banking and his understanding of and contacts across the Asia-Pacific - where many Australian and New Zealand companies are increasingly trading - will add great value to the governance of ANZ," he said.

Before entering politics, Key worked in banking and finance where he was head of global foreign exchange at Merrill Lynch.

ANZ New Zealand's board is rounded out with independents Tony Carter, Mark Berbiest and Joan Withers, and executive directors including local CEO David Hisco, ANZ group chief risk officer Nigel Williams and group CEO Shayne Elliott.