Jacinda Ardern was welcomed by British Prime Minister Boris Johnson in Downing Street, London, on Friday, for talks on security and boosting bilateral ties.
The meeting comes after both leaders attended the NATO summit in Madrid this week.
Johnson's office said he and Ardern will discuss security challenges facing the Indo-Pacific region and the situation in Ukraine.
They are also expected to discuss measures to tackle online disinformation, deepen bilateral trade between the two countries and boost ties in scientific research.
“The partnership between the UK and New Zealand makes both of our countries safer and more prosperous," Johnson said in a statement.
“We are working side by side to address new and evolving threats that threaten to undermine stability and sovereignty in Europe and the Indo-Pacific.”
The UK and New Zealand signed a free trade agreement in February following a similar deal with Australia in late 2021.
The British PM said it was a "great, great pleasure" to welcome Ardern in her first visit since the start of the Covid-19 pandemic.
"I want to say in particular a word of thanks and praise to New Zealand for the very strong line you've taken on Ukraine," he said.
"We've heard a lot about that from you at NATO so that was great. It's very good to see you."
Ardern returned the warm words to her British counterpart, saying the meeting between the two leaders was an "incredibly important milestone".
“The UK is one of Aotearoa New Zealand’s oldest and closest friends and partners. To meet so quickly after New Zealand has reopened its borders reflects the importance we place on our relationship with the UK as we reconnect with the world,” Ardern said.
The two previously met in Madrid ahead of the NATO leaders' summit, which was dominated by the subject of Ukraine.
"I am also very keen to discuss with you Ukraine and the UK's leadership on Ukraine has been significant and obviously we are working together on the training of the Ukrainian forces here in the UK.
"We've also provided our military aid via our partnership with you."
She said the meeting was also a chance to signify to the British people "that we are open for business, for trade, for tourism in particular".
"We want to make sure that our personal invitations are being extended across the breadth of your nation for people to come and see us in beautiful New Zealand.
"So thank you once again."