After he completed his theological studies, Corday left Poitiers to enter the seminary of the Paris Foreign Missions Society on 13 October 1830.

This his first struggle to be faithful to God's call put him in opposition to the wishes of his parents, while maintaining his filial love.

But his stay at the Foreign Missions Seminary in Paris was brief, due to periods of insecurity following the July Revolution.

His intended destination was Sichuan (formerly spelled Szechwan), a province in western China, some 1,250 miles from the coast.

Cornay was secretly ordained to the priesthood three years later on 26 April 1834 by Bishop Joseph-Marie-Pélagie Havard, Coadjutor Apostolic Vicar of Western Tonkin,[2] after traveling along the Red River disguised as a Chinese.

In January 1836, he was told in a letter from the Apostolic Vicar of Szechwan that it was impossible to send him new guides, and gave him the choice between remaining in Tonkin or returning to Macao.

On 20 September 1837, as decreed by the Emperor Minh Mang, he was dismembered and beheaded near the Son-Tay citadel, not far from Hanoi.

Cornay's attempts at missionary work in Vietnam were in direct defiance of Vietnamese law at the time, a fact of which he was aware.

He was canonized by Pope John Paul II on 19 June 1988 as one of the 117 Martyrs of Vietnam, whose feast day is celebrated on 24 November.