Downing Street said the accord will allow the two countries’ forces to deploy together for training, joint exercises and disaster relief.
Die Prime Minister, speaking in Downingstraat alongside his Japanese counterpart, Fumio Kishida, said he is “so glad” the two nations have agreed a reciprocal access agreement (RAA) for armed services.
He said allies in Europe and east Asia have to be unified in the face of “autocratic, coercive powers”.
Mr Kishida’s first official visit to Britain at the invitation of the Government was marked with a guard of honour and an RAF flypast over Horse Guards Parade in central London.
Before holding talks in No 10 op Donderdag, the two leaders stood on a dais as they witnessed a Voyager and two Typhoon fighter jets soar over St James’ Park and the parade ground.
Mr Kishida was then invited in Japanese by the captain of the Nijmegen Company, Grenadier Guards, to inspect the troops.
After the spectacle, Mr Johnson and Mr Kishida headed to Downing Street where the British leader announced that a military accord has been struck.
The Prime Minister said the world has observed the “strong stance” the Japanese government has taken “against the Russian aggression in Ukraine”.
Hy het bygevoeg: “We in the UK recognise that our security in Europe is indivisible from the security, our collective security, in the Asia-Pacific, in the Indo-Pacific region.
“And there is direct read across from the actions of autocratic, coercive powers in Europe, to what may happen in east Asia.
“And that’s why we want to work more closely together.
“And today I’m so glad that we’ve agreed the reciprocal access agreement between our armed services.”
In an account of the meeting issued afterwards by Downing Street, a spokeswoman said the two G7 leaders agreed “democracies around the world needed to stand in unity against authoritarian regimes”.
Geen 10 said the “landmark” RAA will allow the two countries’ forces to deploy together for training, joint exercises and disaster relief.
Officials said the agreement will boost the UK’s commitment to the Indo-Pacific and further safeguard global peace and security, and build on the already close collaboration on defence and security technology between both nations.
Talks began on deepening the UK-Japan defence relationship in September, following on from the Government’s defence and foreign policy integrated review which last year announced a “tilt” towards the Indo-Pacific.
The Government describes Japan as its closest security partner in Asia.
Officials said Tokyo has just two other bilateral visiting forces agreements – one with the United States and the recently agreed RAA signed with Australia in January.
Intussen, Conservative former minister Greg Clark, MP for Tunbridge Wells, was announced as the UK’s new trade envoy to Japan.
Before the meeting, Mr Johnson said he planned to discuss with Mr Kishida the UK-Japan trade partnership, adding that trade relations are “already glorious and increasing” with “co-operation on science, on digital technology and many other things”.
Geen 10 confirmed the Prime Minister discussed working closely with Japan as the UK “progresses its accession to the CPTPP (Comprehensive and Progressive Agreement for Trans-Pacific Partnership) trade bloc” after Brexit.
The Japanese prime minister, speaking with a translator, thanked Mr Johnson for the “warm welcome”, noting that he had made time despite local elections taking place in the UK.
He told the Prime Minister he had been looking forward to a “very fruitful discussion” on the London-Tokyo bilateral relationship, as well as on Ukraine and global affairs.