The British consulate which was closed in Tonga since 2006 will reopen soon.
The move comes as the UK prepares to exit from the European Union within 12 months.
Radio New Zealand International said the United Kingdom is to also open new diplomatic posts in Vanuatu and Samoa.
“They are among nine new posts in Commonwealth countries as part of an expansion of the UK’s overseas network announced by the British Foreign Secretary Boris Johnson,” it said.
Tonga’s diplomatic relationship with Britain could be traced back to 1880 after the Treaty of Friendship between Great Britain and Tonga was signed in 1879.