Ardern said any individual citizens who did go fight for Ukraine would not be prosecuted by New Zealand authorities, but she said it was unwise for them to do so, and consular assistance could not be provided in a war zone.
There were no plans to have NZDF or allied troops cross east from other European countries into Ukraine, she added.
Ardern also pledged $7.5 million for weapons procurement, via the UK.
Asked about the influence of UK Prime Minister Boris Johnson's visit, Ardern said New Zealand was working with a "trusted partner" through the UK.
The measures decided by Cabinet today include:
• The deployment of an NZDF C-130H Hercules transport aircraft and 50 support personnel to Europe – for two months
• A further NZDF 8-person team logistic specialists to support the international donor coordination centre in Germany with the flow of aid and supplies to Ukraine
• An extra $13.1 million, towards military and legal and human rights support, including:
• $7.5m to contribute to weapons and ammunition procurement by the United Kingdom
• $4.1m to support commercial satellite access for the Ukrainian Defence Intelligence
• $1m to the Office of the High Commissioner for Human Rights
• $500,000 for the International Court of Justice and International Criminal Court
Ardern said New Zealand was ready to help Ukraine, as were many other countries.
"The needs of Ukriane remain broad, urgent, and are changing rapidly."
"My expectation is that this contribution will be seen in a similar way to our previous contribution," Ardern said when asked what Russia might make of the latest assistance to Ukraine.
"We already have of course been added to the list of [people] who are subject to a travel ban."
She said the Government was also taking steps to help Ukrainians with satellite imagery, humanitarian, and legal assistance.
"In a war that NZ stands so stongly against, what is the most meaningful contribution we can make?"
Ardern said the goal was to help Ukraine "repel a brutal Russian invasion".
"Such a blatant attack on a country's sovereignty is a threat to all of us and that's why we too have a role to play.
"The global response has seen an unprecedented amount of military support pledged for Ukraine, and more help to transport and distribute it is urgently needed, and so we will do our bit to help.
Ardern said the Russian invasion clearly breached the international rules-based order.
"This is a conflict at great distance from New Zealand but still of significance to New Zealand."
On questions around calling in the Russian Ambassador to the Foreign Affairs, Defence and Trade Select Committee, Ardern said she trusted they would seek and listen to the correct legal advice.
She said there were other more effective options though than targeting the ambassador.
Ardern said there was travel advice against travelling to Ukraine but people were free to travel there if they wished.
Henare said he'd spoken to leaders in the UK who praised New Zealand's efforts.
He added: "We're proud of the contribution we've made to date."
Henare said he had spoken extensively with his UK counterparts to ensure their responses were in step.
Air Marshal Kevin Short, the Chief of Defence Force, said this was the largest deployment to Europe since about 250 personnel were sent to Bosnia in the 1990s.
Short said it was prudent to work with Nato if New Zealand wanted to help get military support to Ukraine.
The CDF said about 20 maintenance staff will travel with the Hercules.
"By the time they deploy on Wednesday and get up, the earliest they could be tasked I'd say would be Monday next week."
New Zealanders who felt strongly about the conflict should not go to Ukraine, but should take comfort in knowing the Government was taking significant steps to help Ukraine, Ardern said.
Ardern said she had no intention to visit Kyiv anytime in the near future.
She said she and the Ukrainian Prime Minister had discussed visiting each other's countries when the timing suited.
On Louisa Wall, Ardern was asked about the departing MP's claims of being unwanted in Cabinet.
"From time to time...I'll be asked on feedback," the PM said.
"What I won't then do is reflect in a public capacity what that conversation entails."
The PM was asked about how Labour managed "spirited" MPs such as Wall.
Ardern said Labour had a large group of talented MPs, adding: "Larger than we have spaces for in our Cabinet."
The PM said she wanted to focus on Wall's achievements, rather than disputes which should be consigned to the past.
Last week, Henare unsuccessfully tried to persuade his Cabinet colleagues to send lethal weapons to help Ukrainian forces, including Javelin anti-tank missiles.
So far New Zealand has focused its efforts in condemning Russia's actions through economic sanctions, and for Ukraine humanitarian support and non-lethal aid to the military, including protective equipment.
It has not yet provided any form of "lethal aid" to Ukraine, usually understood to be weapons, like Javelin anti-tank missiles.
Foreign Affairs Minister Nanaia Mahuta met virtually with Nato foreign ministers on Thursday night.
It came after Ukraine's foreign minister has said he has travelled to Nato HQ in Brussels to discuss one thing: "Weapons, weapons, weapons."
Mahuta told RNZ on Friday New Zealand was limited in terms of the support it could give as part of a multilateral approach.
"We will take a multilateral approach to tackle a range of fronts of this unjust, illegal and unprovoked war that does include military support, that does include humanitarian aid, it includes bringing perpetrators to account at the International Criminal Court and it also includes intelligence and logistical support."
Mahuta said Ukraine's foreign minister had not approached New Zealand directly to ask for lethal military aid but instead spoke generally to countries offering support.
She said the Government was not hesitating to send lethal aid but was instead weighing up how its response would work alongside that of the international community.
Ardern said on Wednesday she thought the distinction around lethal and non-lethal aid was a false one.
"My view is there is almost an artificial distinction here around lethal and non-lethal aid and our contribution to the war in Ukraine," Ardern said.
She cited New Zealand's contribution of intelligence analysts whose work is "directly contributing to the war effort".
Ardern said the distinction between lethal and non-lethal aid was being made by commentators, rather than the Government. It had been suggested the Government could have a moral objection to sending lethal aid and that sending things like Javelin missiles was a line the Government was unlikely to cross.
Act leader David Seymour had previously called on New Zealand to send missile launchers to Ukraine.
Last month, Seymour told Newstalk ZB's Kate Hawkesby that New Zealand needed to step up in a much more serious way to support Ukraine as it fends off attacks by Russian forces.
Meanwhile, National has been calling for Russian Ambassador Georgii Zuev to be expelled since shortly after Russia invaded Ukraine.
Ardern has repeatedly refused, pointing only one other country had done so - Lithuania - and that the Government wanted to keep consular and diplomatic channels open.
RNZ reported today that MPs have been debating whether to order Zuev before Parliament for questioning. That would be an extraordinary move, especially considering he has diplomatic immunity.
Green Party foreign affairs spokeswoman Golriz Ghahraman said Zuev should be expelled if he still refused to appear before the committee.
New Zealand has brought in independent sanctions against Russian oligarchs, officials and their families, as well as a 35 per cent tariff on all Russian imports.
