(1745 – 4 March 1810) was a French Roman Catholic missionary and bishop who served as Vicar Apostolic of Siam from 1786 to 1810.
In 1775, Garnault was imprisoned with Bishop Le Bon, Vicar Apostolic of Siam and father Coudé after several Christian officers refused to consume holy water prepared by Buddhist monks on the occasion of the taking of the oath of loyalty to the king.
With the protection of the Sultan of Kedah, he built a church there, and many Siamese and Portuguese Christians fleeing from Phuket and Ligor arrived and settled in the town.
[2] On his return to Penang, he was surprised to see a large house had been built for him by Light, in his absence, next to the church as a gift on his elevation to bishop.
He was reluctant to travel to Siam or to send missionaries to establish posts there, while his mission also suffered from a lack of funds and priests due to the French Revolution.