Helen Clark, along with more than 30 powerful women, has signed an open letter warning of women's rights being eroded around the world.
The former Prime Minister joined the likes of Irina Bokova, the Bulgarian politician and former UNESCO director, and former Argentinian foreign minister Susana Malcorra, to decry efforts to roll back women's progress.
In some countries, the women said, the push for female rights was seen as something that harmed men, as opposed to an opportunity to change the expectations of both men and women in a way that helped everyone.
- Opinion: Gender equality is not just a fight for women
- Helen Clark talks equality, women and power in new book
- Jacinda Ardern and Helen Clark on confidence and the future for women
"We are deeply convinced that for peace to be achieved and sustained, the full participation of women must be unleashed," the letter says.
"Despite decades of notable advances, a reality in which opportunities, freedoms, and rights are not defined by gender has not been universally attained.
"Even more concerning, we are seeing in some places that the basic rights of women are interpreted as direct and destabilising challenges to existing power structures."
Other female leaders to sign the letter calling for "the need to achieve full gender equality" include former executive secretary of the UN framework convention on climate change, Christiana Figueres, and former Irish president Mary Robinson.
The campaign came about in response to the rise of populism and decline of multilateralism at the United Nations General Assembly in New York last year.
Ms Malcorra, who served a foreign minister from 2015 to 2017, told The Guardian they sensed there was "another wave of pushback on gender equality and gender empowerment that we worked so hard to achieve".
The rise of populism has led to "macho-type strongman" leaders, she said, singling out Brazil, with its new right-wing president Jair Bolsonaro, the Philippines, with its outspoken president Rodrigo Duterte, and other parts of Europe.
She also reflected on the case of abortion in the United States, where there has been a pushback against women having the right to choose.
It comes as US President Donald Trump responded angrily this week to Democrats who blocked a bill from reaching a vote, requiring doctors to use all means available to save the life of a child born alive after an attempted abortion.
Opponents to the Born-Alive Abortion Survivors Protection Act said it was aimed at discouraging doctors from performing legal abortions.
Ms Clark has been a strong defender of women's rights. She shielded Prime Minister Jacinda Ardern from criticism last year when she had her baby, and lauded New Zealanders for being accepting.
"This is a sign of our maturity as a country and its acceptance that combining career and family is a choice which women are free to make."
She faced sexism during her time as Labour leader and then Prime Minister from 1999 to 2008, including criticism over her decision not to have child.
Last year the UN Women National Committee for Aotearoa brought Ms Clark and Ms Ardern together for a conversation to celebrate 125 years of women's suffrage, where both shared concerns about the self-doubt that young women have to overcome.
"Men are much more likely to put themselves forward when they're not fully qualified, whereas women want to be 120 percent qualified - and that's the barrier we've got to get over," Ms Clark said at the time.
A new report by the World Bank found that from a legal standing, only six countries provide men and women with the same opportunities and legislating protections that promote gender equality.