Japan and Tonga have maintained official diplomatic relations since July 1970. Japan is Tonga's leading donor in the field of technical aid. The Japanese government describes its relations with Tonga as "excellent", and states that "the Imperial family of Japan and the Royal family of Tonga have developed a cordial and personal relationship over the years". Japan is one of only four countries to have an embassy in Nuku'alofa, whilst Tonga has an embassy in Tokyo.
In early 2009, Japan became the fourth country to establish an embassy in Tonga (following Australia, New Zealand and the People's Republic of China). In March, Ambassador Yasuo Takase became the first resident ambassador of Japan in Tonga. He was also the first resident Japanese ambassador in any Polynesian country.
In 2013, Tonga's exports to Japan (consisting primarily in pumpkins and tuna) were worth JPY 146 million, while its imports (mainly machinery) were worth JPY 460 million. Japan is Tonga's largest export market.
Japan has sent only bureaucratic diplomats as ambassadors to Tonga. On the other hand, however, one of the Tongan ambassadors is a member of the royal family, Crown Prince Tupouto'a Lavaka (2010–2012).
- "Japan-Tonga Relations", Japanese Ministry of Foreign Affairs
- "King attends reception for new Japanese Embassy" Archived 2011-05-27 at the Wayback Machine, Matangi Tonga, May 30, 2009
- "First resident Japanese Ambassador in Tonga" Archived 2011-05-27 at the Wayback Machine, Matangi Tonga, March 20, 2009
- "Japan to lay out new development assistance to Pacific at PALM". Radio New Zealand International. May 21, 2009. Retrieved October 6, 2011.
- "Pacific Leaders call on Japan for leadership in Water and Sanitation", Matangi Tonga, May 21, 2009
- "Emperor Akihito welcomes Pacific Islands leaders" Archived 2011-05-27 at the Wayback Machine, Matangi Tonga, May 22, 2009
- Tonga’s Crown Prince New Ambassador to Japan | Pacific Islands Report