Johnson greeted Ardern with a handshake outside the door of Number 10 on Thursday, welcoming the New Zealand leader on her first UK trip since the pandemic began.
Inside, with the Union and New Zealand flags in the background, Johnson said it was a "great, great pleasure" to welcome Ardern to Downing Street.
While he said it was her first visit since the Covid-19 pandemic, Johnson also pointed out that it was her first trip since the two countries signed a fresh free trade deal in February.
Johnson praised Ardern for the "very strong line that you take on Ukraine".
Fresh from the Nato summit in Madrid, which she attended alongside Johnson, Ardern said her visit to the UK and Europe, was an "incredibly important milestone for us in New Zealand".
New Zealand only recently reopened its borders to international visitors, after two years of a strict border policy amid the global pandemic.
Ardern said it signified "we are open for business, for trade, for tourism".
The New Zealand prime minister said the pair would be discussing the recently signed trade deal and progress on ratification.
She said the deal was good for both the UK and New Zealand.
Ardern also said they would discuss the situation in Ukraine.
She told Johnson it was a good "opportunity" to discuss the way the two countries have together responded to the war, noting the UK leadership on the conflict.
"We have also provided our military aid via our partnership with you," she said.
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