Thailand and the United Kingdom enjoy longstanding ties of over 400 The English East India Company first arrived in Siam in 1612, during the reign of King Songtham of Ayutthaya and King James I.
Diplomatic relations between Thailand and the United Kingdom were established in 1855, as a result of the Treaty of Amity and Commerce between the British Empire and the Kingdom of Siam. The said Treaty, also known as the Bowring Treaty, was signed in Bangkok on 18 April 1855, during the reign of King Mongkut (King Rama IV) and Queen Victoria.
The United Kingdom established a consulate in Siam in The following year, on 19 November 1857, Phraya Montri Suriyawong, considered Thailand’s first ambassador to the United Kingdom, was granted an audience by Queen Victoria at Windsor Castle to present a letter and gifts from King Mongkut to the Queen. The Siamese Legation in London was established in 1882, with M.C. Prisdang Jumsai serving as ambassador.
Bilateral relations between the two countries have been close and cordial since then, with cooperation expanding in all dimensions. There have also been regular exchanges of visits between the two sides at all levels, including that of the royal families.
Thailand and the UK's bilateral relations have been elevated to that of a strategic partnership. In March 2024, H.E. Mr. Parnpree Bahiddha-Nukara, Deputy Prime Minister and Minister of Foreign Affairs of Thailand, and the Right Honourable Lord Cameron of Chipping Norton, Secretary of State for Foreign, Commonwealth, and Development Affairs of the United Kingdom, signed the UK–Thailand Strategic Partnership Roadmap during the latter’s visit to Thailand. The partnership aims to strengthen the relationship of the two countries at bilateral, regional and multilateral levels in all areas including political, security, trade and investment, agriculture, climate and energy, science and technology, health and people-to-people links.
Thailand and the United Kingdom celebrated the 170th anniversary of the establishment of diplomatic relations between the two countries in 2025. Throughout the year, both sides organised a range of commemorative activities, including a reception to mark the anniversary of diplomatic relations; the photo exhibition “Siam through the Lens of John Thomson”; the publication of a commemorative book; and the Thai textile exhibition “Chud Thai through the Ages: Weaving History, Craft, and Identity.” Her Royal Highness Princess Sirivannavari Nariratana Rajakanya graciously presided over the opening of the exhibition and presented royal attire, including traditional Thai national costumes and various Thai textile ensembles of her own design. The British Embassy Bangkok also organised a commemorative concert performed by His Majesty King Charles III’s Royal Marines Band in June 2025 at Vajiravudh College, which was graciously attended by His Majesty the King and Her Majesty the Queen.
At present, the ‘Thailand-United Kingdom Strategic Dialogue’ serves as the main high-level forum for regular consultations between the two sides on areas of bilateral collaboration as well as on regional and global issues of mutual interest. Meeting at the level of Vice Minister of Foreign Affairs, the inaugural session of the Strategic Dialogue took place on 20 May 2013 in Bangkok. The most recent meeting--the Fifth Strategic Dialogue--was held on 21 April 2025, co-chaired by H.E. Mr. Russ Jalichandra, Vice Minister for Foreign Affairs, and H.E. Mrs. Catherine West, Minister for the Indo-Pacific of the Foreign, Commonwealth and Development Office of the United Kingdom. The Thai-United Kingdom Parliamentary Friendship Group has also been set up as a mechanism to promote parliamentary ties.
Thailand and the United Kingdom have developed close defence and security ties, with cooperation covering wide-ranging areas including defence procurement, military education and training. Both sides have worked together on traditional and maritime security as well as non-traditional security, such as cyber security and humanitarian assistance. The two sides also conduct joint military exercises called 'Panther Gold’ as well as take part in 'Cobra Gold.' The latter is the largest multi-national military exercise in the region held annually in Thailand. In 2022, both sides signed a Memorandum of Understanding on Defence Cooperation, which serves as an important framework for further joint exercises, regular bilateral talks and sharing best practice.
In addition to bilateral cooperation, Thailand and the United Kingdom also cooperate at the regional level through ASEAN, following the United Kingdom’s accession as an ASEAN Dialogue Partner in 2021. ASEAN and the United Kingdom endorsed the ASEAN–UK Plan of Action (PoA) 2022–2026 at the ASEAN–UK Foreign Ministers’ Meeting in August 2022, which serves as a framework for guiding cooperation between the two sides. Subsequently, in 2023, the United Kingdom announced programmes to implement cooperation with ASEAN under the PoA in five priority areas: (1) support for economic integration; (2) climate change; (3) public health, particularly capacity-building in the surveillance, prevention, and treatment of communicable diseases; (4) the Women, Peace, and Security (WPS) agenda; and (5) education for women and girls. ASEAN and the United Kingdom are scheduled to celebrate the fifth anniversary of their partnership in 2026.