Green MP Eugenie Sage is not standing for the party co-leadership because she wants to focus on her ministerial portfolios of conservation, land information, and associate environment.
The final nominations for the co-leadership were announced today and Marama Davidson and Julie Anne Genter are the only two candidates.
Sage was widely considered to be a contender, but said in a Facebook post she would not be running.
"The next three years are crucial to the future of the Party. Being part of government for the first time we can create real change that helps nature thrive, reduces our human footprint on the environment, and shifts the economy to a sustainable footing," Sage said,
"I am 110 per cent committed to my new roles as Minister of Conservation, Land Information and Associate Environment with responsibility for waste.
"Conservation and environmental issues are central to the Green Party kaupapa. I believe my energy and skills are best used ensuring there is a strong Green heart to our new kotahitanga government, so we make decisions where nature and a healthy environment really matter."
The two-horse race gives Green delegates, who are chosen by members, a clearer choice.
Davidson is considered a strong social justice advocate and an MP outside the executive, giving her more freedom to criticise the Labour-led Government on issues where the Greens disagree.
Genter's strengths are seen as her competence on financial and economic issues as well as core Green issues such as climate change, and she has said that criticising the Government can be more powerful coming from a minister in the executive.
She concedesshe will not be able to speak against the Government in her portfolio areas of women, associate transport and associate health.
Both Davidson and Genter, in putting their hands up for the job, stressed the importance of carving out an independent voice for the Greens.
Davidson referred to the Greens opposition to the TPP, while Genter said the party could have done better to address concerns in the membership over the party's support for the Government's waka-jumping bill.
Davidson, 44, also made a point of talking about diversity, and has been compared with previous co-leader Metiria Turei, a Maori woman who had a particularly strong voice on welfare reform and social justice issues.
Genter, 38, said she had broad appeal and had held a wide range of portfolios during her time with the Greens, which would be an asset to grow the Green's share of the vote.
They will now campaign across the country, including a session at the Green Party policy conference in Napier on March 3.
They will hold a conference call on March 25, where Green delegates will have a chance to grill each candidate. The campaign will finish on March 26, and delegates will cast their ballots from then until April 7.
The winner will be announced on Sunday April 8.
Turei resigned in August last year after she admitted to historical fraud offending while on the benefit 20 years ago.
She said the scrutiny of her family over her past welfare history had become unbearable.
She retired from Parliament after last year's general election.
Co-leader James Shaw led the party through the election alone.
The circumstances around the death are being treated as unexplained.