"We may be geographically distant but we are true partners as well in building and sustaining international peace and security, and promoting and defending an open, inclusive and rules-based international order," Ardern said.
"This international environment is an uncertain and challenging one in the face of isolationism and protectionism. New Zealand and the EU share an understanding that going it alone in an interconnected and interdependent world is just not feasible."
Tusk said a free trade deal between New Zealand and the EU would be of "enormous strategic importance for the rules-based international order, at a time when some are questioning it".
"We are sending a clear message that we stand together against protectionism."
Promoting a free trade agreement with the EU is the main purpose of Ardern's trip to Europe, where she has spent this week firstly London and then at the World Economic Forum in Davos.
Following her meeting with Tusk, Ardern met European Commissioner for Agriculture and Rural Development Phil Hogan and European Commission President Jean-Claude Juncker, who said he hoped an FTA would be completed by the end of this year.
"We should do everything possible to conclude the trade agreement between New Zealand the EU in the course of this year," Juncker said after their meeting.
"I'm convinced, given the good spirit that did impact our discussions today, that this is possible. New Zealand is far on the map, but close to our hearts."
Hogan will visit New Zealand next month, and both he and Ardern commented on how quickly the negotiations were proceeding - but Hogan added that there remained "sensitive issues on both sides".
An FTA with the EU has been estimated to boost New Zealand's annual GDP by $2 billion and increase exports by up to 20 per cent.
One of the trickier aspects of the negotiations is reducing tariffs on New Zealand's agricultural products, including red meat.
Besides the US, the EU is the largest trading partner that New Zealand does not have an FTA with. In 2017, New Zealand exports to the EU added up to $5.2 billion, while imports from the EU totalled about $10.7 billion.
Ardern and Tusk also talked about working together on global security and - in another veiled attack on the US, which has pulled out of the Paris Agreement - the importance of ambitious climate change targets.
Ardern said it was critical to implement carbon emissions targets, but also to "push our partners to lift ambitions".
Tusk praised the close relationship between New Zealand and the EU.
"Geographically we are far apart, but politically and economically we are close partners and friends.
"Let me borrow from the Māori wisdom and say: let us keep close together, not far apart. In the current uncertain global environment, the friendship between the European Union and New Zealand is priceless."
