Diplomatic relations with France and Thailand cover a period from the 16th century until modern times. Relations started in earnest during the reign of Louis XIV of France with numerous reciprocal embassies and a major attempt by France to Christianize the Kingdom of Thailand (then known as Siam) and establish a French protectorate, which failed when the country revolted against foreign intrusions in 1688. France would only return more than a century and a half later as a modernised colonial power, engaging in a struggle for territory and influence against Thailand in mainland Southeast Asia that would last until the 20th century. France established a protectorate over the Kingdom of Cambodia in 1863, pressuring Siam to renounce its claims over the region. 30 years later, following the Franco-Siamese crisis and the Paknam naval incident in 1893, Siam was forced to cede all territories east of the Mekong River (which constitutes most of modern Laos) to France under Franco-Siamese Treaty, which then established as the French protectorate as part of Indochina. Following their independence from France in 1953, both Cambodia and Laos fell of the communist takeovers in 1975 such as the Khmer Rouge (Cambodian Reds) in Phnom Penh and Pathet Lao in Vientiane with rise of Marxist–Leninist ideologies, and the aftermaths of their revolutions differed drastically, transforming the geopolitics following the Second Indochina War alongside Vietnam after the Fall of Saigon to the Viet Cong at the end of the Vietnam War in April 1975 and the Vietnamese unification in July 1976, with Saigon renamed "Ho Chi Minh City" in honor of the late revolutionary leader who defeated both French colonialism and the American imperialism like other communist leaders such as Saloth Sâr ("Pol Pot", a French phrase for Politique Potentielle) and Souphanouvong fought to establish a new systems in Indochina by their visions of a socialist paradise.

16th–17th century relations

First French Catholic missions

The first instance of France-Thailand contacts is also the first historical record of an attempt to introduce Christianity to Siam: according to Giovanni Pietro Maffei, about 1550 a French Franciscan, Bonferre, hearing of the great kingdom of the Bagoans and the Thai in the east, went on a Portuguese ship from Goa to Cosme (Bago), where for three years he preached the gospel without any result. The Catholic encyclopedia, p. 766

The first major contacts between the two countries occurred after Thailand was made an apostolic vicariate by Pope Alexander VII on 22 August 1662. The mission was assigned to the newly formed Paris Foreign Missions Society to evangelize Asia, and Siam became the first country to receive these efforts, to be followed by new missions 40 years later in Cochinchina, Tonkin and parts of China,Missions, p. 4 because Siam was highly tolerant of other religions and was indeed the only country in Southeast Asia where the Catholic Fathers could establish themselves safely.Les Missions Etrangeres, pp. 45, 122

Monseigneur Pierre Lambert de la Motte, Bishop of Beirut, Vicar-Apostolic of Cochinchina, and member of the Missions Etrangères de Paris, accompanied by Fathers De Bourges and Deydier, Catholic Encyclopedia left Marseille on 26 November 1660, and reached Mergui 18 months later. He arrived in the Ayutthaya Kingdom in 1662. Thai Ministry of Foreign Affairs

In 1664, a group of missionaries led by François Pallu, Bishop of Heliopolis, also of the Paris Foreign Missions Society, joined Lambert in the capital city of Ayutthaya after 24 months overland travel and started missionary work. In 1665–66 they built a seminary in Ayutthaya with the approval of King Narai,The Cambridge History of Christianity by Stewart J. Brown, Timothy Tackett, p. 464 the Seminary of Saint Joseph (later Seminary of the Holy Angels, at the origin of the College General, now in Penang, Malaysia).

In 1669, Louis Laneau, Bishop of Motella, also a member of the Paris Foreign Missions Society, was named head of a Roman Catholic mission in mainland Southeast Asia, with his headquarters at Ayutthaya. They propagated the Christian faith and also took care of Annamite Christians and Japanese Christian communities in Thailand. Narai welcomed these missionaries, providing them with land for a church, a mission-house and a seminary (St. Joseph's colony). Bishops Lambert and Ballue established a Western hospital in Thailand in 1669 at Ayutthaya, with Father Laneau as the head doctor. The hospital provided medical care to about 200–300 people daily.History and evolution of western medicine in Thailand Somrat Charuluxananana, Vilai Chentanez, Asian Biomedicine Vol. 1 No. 1 June 2007, p. 98

During a 1670 trip to France, Pallu obtained from Louis XIV a letter to King Narai, which, together with a letter from the Pope, he remitted in Ayutthaya in October 1673 and which was received with great reverence.

These contacts were closely associated with the development of French influence in South Asia, and especially with the establishment of the French East India Company in 1664, and the development of colonial French India.

First trade contacts (1680)

In 1680, the newly formed French East India Company sent a ship to Thailand, bearing a trading mission led by André Deslandes-Boureau, son-in-law of the Governor General of the French settlement in Pondicherry François Martin, which was well received by the Thais.Smithies 2002, pp. 7–185

In September 1680, a ship from the French East India Company visited Phuket and left with a full cargo of tin. The Dutch, the English, and from the 1680s the French, competed with each other for trade with the island of Phuket (the island was named Junk Ceylon at that time), which was valued as a rich source of tin. In 1681 or 1682, Siamese King Narai, who was seeking to reduce Dutch and English influence, named Governor of Phuket the French medical missionary Brother René Charbonneau, a member of the Siam mission of the Société des Missions Etrangères. Charbonneau held the position of Governor until 1685. New Terrains in Southeast Asian History, Abu Talib, p. 294

In a series of missions back and forth each side honoured its kings and celebrated its artistic achievements, and learned to appreciate the other's. The delegations sought to foster more commerce and elevate their prestige and on the global stage. Artists in Paris produced scores of prints depicting the Siamese diplomats and the lavish receptions at Versailles and Ayutthaya. Thousands of art objects – especially mirrors, porcelain, textiles, and metalwork – were exchanged.Meredith Martin, "Mirror Reflections: Louis XIV, Phra Narai, and the Material Culture of Kingship." Art History 38.4 (2015): 652–667.

First Thai embassies to France (1680 and 1684) King Narai further sought to expand relations with the French, to counter Portuguese and Dutch influence in his kingdom, and at the suggestion of his Greek counselor Constantine Phaulkon. In 1664, the Dutch had used force to exact a treaty granting them extraterritorial rights as well as freer access to trade. In 1680, a first Siamese ambassador to France was sent in the person of Phya Pipatkosa on board the Soleil d'Orient, but the ship was wrecked off the coast of Africa after leaving Mauritius and he disappeared.

A second embassy was sent to France in 1684 (passing through England), led by Khun Pijaiwanit and Khun Pijitmaitri, requesting the dispatch of a French embassy to Thailand. They met with Louis XIV in Versailles. In response, Louis XIV sent an embassy led by the Chevalier de Chaumont.

Embassy of Chevalier de Chaumont (1685)

The Chevalier de Chaumont was the first French ambassador for King Louis XIV in Siam. He was accompanied on his mission by Abbé de Choisy, the Jesuit Guy Tachard, and Father Bénigne Vachet of the Société des Missions Étrangères de Paris. At the same time, he returned to Siam the two ambassadors of the 1684 First Siamese Embassy to France. Asia in the Making of Europe By Donald F. Lach, p. 253

Chevalier de Chaumont also brought a group of Jesuit mathematicians (Jean de Fontaney (1643–1710), Joachim Bouvet (1656–1730), Jean-François Gerbillon (1654–1707), Louis Le Comte (1655–1728) and Claude de Visdelou (1656–1737))Eastern Magnificence and European Ingenuity: Clocks of Late Imperial China, Catherine Pagani (2001), p. 182 whose mission was to continue to China to reach the Jesuit China missions. Le Comte remain in Siam with King Narai, but the others reached China in 1687.

Chevalier de Chaumont tried without success to convert Narai to Catholicism and to conclude significant commercial treaties. A provisional agreement was signed to facilitate trade between France and the Royal Warehouse Department. France also received a tin monopoly in Phuket, with Chaumont's former maître d'hôtel Sieur de Billy named governor of the island, and received the territory of Songkla in the south.

When Chaumont returned to France, Count Claude de Forbin, who had accompanied Chaumont with the rank of major aboard the Oiseau, was induced to remain in the service of the Siamese king, and accepted, though with much reluctance, the posts of grand admiral, general of all the king's armies and governor of Bangkok. His position, however, was soon made untenable by the jealousy and intrigues of the minister Constantine Phaulkon, and after two years he left Siam, reaching France in 1688. He was replaced as Governor of Bangkok by the Chevalier de Beauregard.English intercourse with Siam in the seventeenth century, John Anderson (2000), p. 365

The French engineer Lamarre also remained in Siam at the king's request in order to build fortifications. He began by building a fortress in Bangkok, and designed fortifications for Ligor (Nakhon Sithammarat), Singor (Songkhla), Phatthalung, Ayutthaya, Louvo (Lopburi), Mergui, Inburi and Thale Chupson.

Second Thai embassy to France (1686)

A second Thai embassy, led by Kosa Pan, was sent to France to ratify the treaties. The embassy accompanied the returning embassy of Chevalier de Chaumont and traveled on the boats l'Oiseau and la Maligne. It brought a proposal for an eternal alliance between France and Siam and stayed in France from June 1686 to March 1687. Kosa Pan was accompanied by two other Siamese ambassadors, Ok-luang Kanlaya Ratchamaitri and Ok-khun Si Wisan Wacha, and by the Jesuit Father Guy Tachard.

Kosa Pan's embassy was met with a fair reception and caused a sensation in the courts and society of Europe. The mission landed at Brest, France and traveled overland to Versailles, constantly surrounded by crowds of onlookers.

The "exotic" clothes as well as manners of the envoys (including their kowtowing to Louis XIV during their visit to him on 1 September), together with a special "machine" that was used to carry King Narai's missive to the French monarch caused much comment in French high society. Kosa Pan's great interest in French maps and images was commented upon in a contemporary issue of the Mercure Galant. Suarez, p. 29

The main street of Brest was named Rue de Siam in honour of the embassy.

Siam–England war (1687)