Johnson and Ardern recently met at the Nato Summit in Madrid, Spain.
Ahead of their meeting, Johnson, who has been a keen proponent of wider free travel around the Commonwealth, announced planned agreements included extension to the Youth Mobility Scheme and a new science and innovation partnership.
The current scheme allows Kiwis and British people aged under 30 to work in the other country for up to two years.
PM Jacinda Ardern meets with UK PM Boris Johnson in London. Photo / Thomas Coughlan
Johnson said in a statement the extension would raise the age limit and increase the length of visas, attracting and allowing "highly skilled and ambitious young people to move between the two countries easily, sharing skills and innovative ideas between the two countries".
PM Jacinda Ardern meets with UK PM Boris Johnson in London. Photo / Thomas Coughlan
Ardern is greeted by Johnson outside Downing Street in London. Photo / Thomas Coughlan
The visit comes after both leaders attended the Nato summit in Madrid this week, and follows the agreement of the UK-New Zealand free trade deal in February.
Two-way trade was worth about $6 billion in the year to March 2020. It was New Zealand's seventh-largest trading partner pre-Covid.
The two leaders are also expected to discuss geo-political challenges, such as security challenges facing the Indo-Pacific and the situation in Ukraine, and agree new measures tighten the UK-New Zealand alliance.
"Though they may be one of our most distant allies, the United Kingdom counts New Zealand among our closest friends," Johnson said.
"We share a world view, standing up for democracy and free trade around the world, which is fortified by deep bonds of language and culture.
"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.
"Our trade deal is slashing red tape, cutting tariffs and opening exciting new opportunities for British businesses and entrepreneurs to travel and trade.
"And now our scientists are working together to solve humanity's toughest challenges."
Commitments are also expected around working together on online safety, by increasing information sharing and best practice, with a focus on disinformation and safeguarding users, and underlining their leading global roles in tackling online harm.
Prime Minister Jacinda Ardern and Belgium Prime Minister Alexander De Croo at the Nato summit in Madrid, Spain. Photo / AP
Trade ties between the two countries will also be on the agenda, including the UK's accession to the Comprehensive and Progressive Agreement for Trans-Pacific Partnership (CPTPP), and the recently agreed Free Trade Agreement.
It is the first bilateral meeting between the two prime ministers in either Britain or New Zealand.
Ardern's last visit to the United Kingdom was in January 2019, when she met then British Prime Minister Theresa May to discuss post-Brexit trade.
Ardern previously said her meeting with Johnson would help "reconnect" the countries and provide updates on any progress since the NZ-UK FTA was signed in March.
The Government aims to ratify the deal by the end of the year. Legislation was introduced to Parliament last week.
Ardern will also meet with Prince William, the Duke of Cambridge, and speak at the Chatham House think-tank, while in London.
