Westpac holds the New Zealand government's banking contract, media reports said.  

Power joins the bank in January next year after the end of his term as parliament member for Rangitikei, where he has been for the past 12 years. He had also functioned as cabinet minister for the last three years, including as minister of commerce and associate minister of finance. He is leaving politics at the 26 November election.

"This is the beginning of a new and exciting chapter in my career," said Simon Power in a media release.

He replaces Richard Jarrett, who has been in the role since 2006.

Westpac Private Bank deals with premium private clients with at least NZ$250,000 in household income and NZ$1 million in assets.