New Zealand First deputy leader Peter Brown has quit his post at a conference in Auckland.
He resigned at the conference, called to discuss the party's future after its disappointing election campaign last year.
Mr Brown, deputy leader for 10 years, will remain a party member, and also backs Winston Peters to continue leading the party.
NZ First failed to reach the 5 percent party vote threshold in last year's election, and Mr Peters was well beaten by National's Simon Bridges in the Tauranga electorate.
"In simple terms, I was very disappointed and somewhat disillusioned with our campaign and the results at the last election, and I couldn't shake that mood off," Mr Brown told NZPA.
"And I decided, well if I can't shake it off, I'm better to hand it over to someone who's got the necessary vitality to build the party up again."
There had been a frank discussion at the meeting of around 100 party members about their concerns, but people were equally determined that the party could and should continue, he said.
"(They were) very buoyant and very proud, that's the only word I can use, about the party's achievements - so I think there's a lot of hard work for them ahead but I think they can do it."
It was confirmed last month that Winston Peters would continue to lead NZ First in the near future.
"Winston's got a lot going for him as a politician, he's very good, he's got a political mind -- like everybody he makes mistakes, but it would be mad just to dispense with him," Mr Brown said.
Last year, Mr Peters become embroiled in investigations into donations to NZ First, and while no breaches of the law were found, the scandal took a heavy toll on the party and his race for Tauranga.
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