In 1552 Francis Xavier, writing from Sancian to his friend Diego Pereira, expressed his desire to go to Siam, but his death on 2 December 1552, prevented him.

In 1606 the Jesuit Balthasar de Sequeira, at the request of the Portuguese merchant Tristan Golayo, and in 1624 Father Julius Cesar Margico, came to Ayutthaya and gained the favour of the king.

A subsequent persecution, however, stopped the propagation of the Christian faith and no missionaries were allowed until Siam was made a Vicariate Apostolic by Pope Alexander VII on 22 August 1662.

Siam, in those days a rendezvous of commercial enterprise in the East, gave shelter to several hundred Annamite and Japanese Christians who had been expelled or lived there as exiles due to persecutions at home.

Pallu, on his return to Rome (1665), obtained a Brief from Pope Clement IX (4 July 1669), by which the Vicariate of Siam was entrusted to the newly founded Society of Foreign Missions of Paris.

King Phra Narai gave the Catholic missionaries a hearty welcome, and made them a gift of land for a church, a mission-house, and a seminary (St. Joseph's colony).

Through the influence of the Greek or Venetian, Constantine Phaulkon, prime minister to King Narai, the latter sent a diplomatic embassy to Louis XIV in 1684.

However, after the departure of M. De Chaumont, a Siamese nobleman, Phra-phret-racha, instigated a revolution in which Greece's Minister to Ayutthaya was murdered, King Naraï deposed, Msgr.

On 8 July 1856, King Mongkut signed a political-commercial treaty with France, by which the privileges granted to the Catholic missionaries by Phra-Naraï in the 17th century were renewed.

Thanks to the broad-mindedness of Kings Mongkut (1851–1868) and Chulalongkorn (1868–1910), the Catholic Church in Siam enjoyed peace under Pallegoix's successors, Bishops Dupont (1862–1872) and Vey (1875–1909).

At the beginning of the 20th century, there were about 23,000 Catholic believers, 55 churches and chapels, representatives of such monastic orders, social and educational institutions (e.g., orphanages, schools and a seminary, college).

[14][15] While in Thailand he had audiences with the prime minister, King Vajiralongkorn, and the supreme Buddhist patriarch, as well as celebrating masses at the National Stadium and Assumption Cathedral.