Marama Davidson has been elected new female co-leader of the Green Party.
The party made the announcement on Sunday morning, following months of speculation and voting.
Ms Davidson, 44, defeated rival Julie Anne Genter, 38, who has ministerial roles in the present Government.
Ms Davidson has been an MP since 2015, and is from the social justice wing of the party - considered by some to be the heir to former leader Metiria Turei.
She spent a decade working with the Human Rights Commission before becoming an MP, and said not having a ministerial role will give her more room to criticise Labour.
"It is the greatest honour of my life," she told the party faithful at Pioneer Women's Hall in Auckland, before heaping praise on her defeated opponent.
"There could be no one better to have on your team with your skills, your experience, your political nous and someone who is doing such an amazing job."
Ms Genter congratulated Ms Davidson in a tweet.
"She brings incredible mana and an important perspective to our political leadership. I am very proud to stand with her in caucus and continue our work to protect our people and planet."
Ms Davidson said it was "truly humbling" to win the co-leadership.
She said she would fight for the "many mummas" who don't have the support she has, and took shots at the "fiscal and moral" hole left behind by the previous National Government.
Her number one goal would be to ensure the Greens don't lose support while being in Government, as has happened to smaller coalition members in the past.
James Shaw has been leading the party alone since Ms Turei's resignation ahead of last year's election.
As opposed to the straight majority caucus vote used by National when electing a leader, the Greens use a delegate system. Each branch of the party across the country puts forward delegates based on the size of their electorate.
Ms Davidson is the party's third female co-leader in its 23-year history, after Jeanette Fitzsimons and Ms Turei.