Marama Davidson says it is the greatest honour of her life to have been elected as the co-leader of the Green party.
She paid tribute to the defeated candidate, Julie Anne Genter, and said her respect for her had grown during their contest.
Ms Davidson said her main goal will be to ensure that the Greens do not lose support as a result of being in coalition.
The Greens must remain strong, cohesive and united in the drive for change, she said.
"In order to be a genuine and relevant voice for modern Aotearoa, we need to reflect its diverse reality," Ms Davidson said.
"We need more members from all backgrounds and communities. We need to be present in multicultural, Māori and Pasifika communities, in provincial and rural communities, and in the suburbs, with women, young people and workers."
National had left the country in a worse condition than expected, she said
Referring to the revelation of rot in the walls of Middlemore Hospital, she said National had been more interested in surpluses than having safe conditions in hospitals.
She said the Greens needed to go further, and be even bolder, and could return at 2020 with more MPs.
Many smaller parties in Governing arrangements struggle to retain support, but she said her number one goal was to make sure that doesn't happen to the Greens.
"We can't have clean rivers, we can't save our native species, we can't lift our families out of poverty, we can't build warm dry homes ... If our party isn't cohesive and strong and campaigning for change."
The Green Party needed to work on representing a broad cross-section of New Zealanders, as well as regaining the trust and support of those who didn't vote for the party in 2017.
Co-leader, James Shaw, said after eight months leading the party alone, he was looking forward to having someone to share the job with.
He said Ms Davidson "lit a wildfire through the party" during her leadership campaign.
The announcement was made in Auckland this morning.
The Green Party's constitution dictates it must have both a male and female co-leader.
The female position became vacant after Metiria Turei resigned in the run up to last year's General Election after revealing she had committed benefit fraud.
The two MPs had been campaigning for nearly two months and roughly 150 branch delegates voted.
Ms Davidson, 44, is a Green MP who does not hold any Ministerial roles. She has been a MP since 2015.
She is of Ngāti Porou, Te Rarawa, and Ngāpuhi descent. She's the daughter of the actor Rawiri Paratene.
She is a graduate of the University of Auckland, and of Te Whare Wanaga o Awauiarangi, worked for 10 years at the Human Rights Commission, and was chief panelist for the Glenn Inquiry into Domestic Violence and Child Abuse.
She lives in Manurewa and has six tamariki.
Launching her bid for the campaign, she promised to grow the Green Party with bold and brave leadership and by reaching out to communities who have not traditionally supported the Greens.