Roman Catholic missionary whose efforts to advance French interests in Vietnam were regarded as important by later French colonizers.

Pigneau de Béhaine left France in 1765 and went to establish a seminary in southern Vietnam, then known as Cochinchina. He arrived at Ha Tien, near the Cambodian frontier, in 1767, and he remained there for two years, preparing Vietnamese pupils for the priesthood, until the seminary was destroyed in a Siamese (Thai) invasion. He then escaped to Malacca with several of his students and reestablished the school in Pondicherry, India. He was made titular bishop of Adran in 1770, and about that time he left India and returned to Macau, where he compiled a dictionary and wrote a catechism in Vietnamese.

In 1774–75 Pigneau de Béhaine made his way back to Cochinchina via Cambodia. He remained at Ha Tien until 1777, when the rebel Tay Son brothers overthrew the seigneurial Nguyen family and orphaned the young heir, Nguyen Phuc Anh. In 1782, after Nguyen Anh's (Gia Long) first attempt to regain control of the south had ended in disaster, the bishop met and befriended Nguyen Anh on the French-held island of Kah Kut, near Phu Quoc, for which he won the future king's enduring gratitude. The bishop returned to France in 1787 and persuaded King Louis XVI to sign a treaty with the Vietnamese prince, but he was unsuccessful in his attempts to obtain armaments and troops to reinstate his protégé. Undaunted, he returned to India, where he won support from French merchants for Nguyen Anh's cause. Unofficial French assistance played a significant, but not predominant, part in Nguyen Anh's successful battle to overcome the rebels. He became the emperor Gia Long over a united country in 1802.

Pigneau de Béhaine assisted Nguyen Anh in both foreign and domestic matters while the future emperor fought to extend his power over the whole country. The bishop was never able to convince him to do more than grudgingly tolerate Christian missionary work in Vietnam during his lifetime. After a long illness, Pigneau de Béhaine died, and he was buried with military honours in Saigon.