Prime Minister Jacinda was one of a number of high-profile guests, including US Vice President Kamala Harris, to address the European Union Parliament for International Women's Day.
"We need to stick together because we are all in this together," Ardern told MPs via video yesterday (NZ time).
She said Covid-19 had exacerbated structural inequalities between women and men.
"Only by fully – and meaningfully – including women in leadership at all levels can we ensure that our responses to the pandemic meet the needs of everyone."
She said that as leaders, "we will be tested".
"We must resist the false promises in the face of those tests of protectionism and nationalism in our recovery from Covid-19.
"We must also do more to support women-led business to be part of the recovery, so they can more readily experience the benefits of trade."
Ardern was followed by Harris – the first female Vice President of the United States.
"We must ensure women's safety at home and in every community.
"We must treat them with dignity at work and put in place the structures needed so that they can both care for their families and excel in the workforce."
And she said that women need to have an equal voice in decision-making – this, she said, is essential to free and fair democracies.
"This not just an act of goodwill; this is a show of strength. If we build a world that works for women, our nations will all be safer, stronger and more prosperous."
The session in the EU Parliament focussed on women's empowerment and leadership during the Covid-19 pandemic.
In his opening speech, European Union President David Sassoli said: "The pandemic risks wiping out decades of achievements gained by European women's struggle for the right to work, to share care work, for autonomy, for respect and for the right to make their own choices."