Anastase Douay was born in La Quesnoy, Belgium. He became a priest and joined the expedition to the America that was led by Robert Cavalier de La Salle, which left La Rochelle, France, in 1684. They established a French colony in Texas but when La Salle was murdered by his own men in 1687, Douay moved to Quebec before returning to France.
Douay went to America again in 1699 where he successfully found the mouth of the Mississippi. It is believed that Douay died in Mexico.