The Mana byelection will take place on November 20, Prime Minister John Key has announced.
Outgoing Mana MP Winnie Laban is to take up a post with Victoria University.
Mr Key admitted National was the underdog but said Hekia Parata was an "excellent candidate."
Labour has announced former TVNZ journalist Kris Faafoi as their candidate. Mana is a labour safe seat.
"As Labour MP Winnie Laban has given notice, her resignation will be effective from Friday 15 October. I have been advised it is appropriate to now set a date for the by-election," Mr Key said.
"This means that Writ Day will be Wednesday 20 October. The last date for candidate nominations to be received will be Wednesday 27 October, and the last day for the return of the Writ will be Thursday 9 December 2010."
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