Jean Cavelier, priest and adventurer, was born in Rouen, France, in St. Herbland parish. He was the older brother of René Robert Cavelier, Sieur de La Salle, and accompanied him on the French expedition that landed at Matagorda Bay, Texas, in February 1685. The parents had one other son, Nicolas, and a daughter who married Nicolas Crevel. The father, also named Jean, and his brother, Henri, were wealthy merchants at Rouen, "living more like nobles than burghers."
The younger Jean Cavelier became a Sulpician priest. He migrated to Canada in 1665 and served as curate at Montreal. A year later he influenced his younger brother Robert to join him there, thus opening the door to La Salle's career as an explorer. Abbé Cavelier handled some of La Salle's business affairs and advanced him capital to engage in the fur trade. In 1679 the abbé went to court to collect what his brother owed him, which amounted to more than the value of all the peltries La Salle had shipped to Montreal. Cavelier also resorted to intercepting La Salle's mail. "In his double character of priest and elder brother," says Francis Parkman, "he seems to have constituted himself the counselor, monitor, and guide of a man who, though many years his junior, was in all respects incomparably superior to him."
Despite the bitterness thus engendered, Cavelier joined the La Salle expedition to the Gulf of Mexico and shared in its hardships. He wrote a journal of that undertaking, but ended it more than a month before La Salle was murdered in eastern Texas. The accuracy of the document has often been questioned.
In the fall and winter of 1685–86 Abbé Cavelier accompanied his brother on a mysterious trek west of Matagorda Bay, the journal account of which is both confusing and at odds with La Salle's equally obfuscatory version. He was also among the seventeen who accompanied La Salle on a journey intended to reach Fort Saint Louis of the Illinois in January 1687. After the murder of La Salle and their nephew Crevel de Moranget, in March 1687, the abbé feared for his own life. He and his nephew, Colin Cavelier, were visited following La Salle's death by the murderer, (Pierre) Duhaut, who "told them that they could withdraw and go wherever they wished, for he would not be able from then on to see them without pain."
Cavelier, his nephew, and five others at last resumed the march for the Illinois post, to proceed thence to Canada and France. In the spring of 1688, Henri de Tonti, having searched for La Salle at the mouth of the Mississippi, returned to Fort Saint Louis of the Illinois to find Cavelier and his associates. To obtain a loan from La Salle's funds for the voyage to France, the abbé concealed from Tonti his brother's death, assuring him that La Salle was in good health in his Gulf Coast colony. Not until a year later did Tonti learn the truth. In the meantime, all possibility of rescuing the more than twenty colonists who had remained at Fort St. Louis of Texas was removed by the Karankawa Indians, who destroyed the settlement late in 1688.
On reaching Montreal in July 1688 Cavelier and his nephew remained for a time, while the others went on to Quebec to be lodged in the Recollect monastery. They sailed together for France on August 21, 1688. Their ship docked at La Rochelle on October 9.
A few years later, as a clamor arose for renewal of La Salle's Mississippi valley enterprise, Cavelier added his voice, warning that if the English seized control of the Mississippi River, they also would gain the Illinois and Ottawa Indians, and "all the nations with whom the French of New France carry on trade." He nevertheless declined to join the expedition of Pierre Le Moyne, Sieur de Iberville, which left France for Louisiana on October 24, 1698.
Sometime after Iberville's second voyage to Louisiana, he received an inquiry from Abbé Cavelier-perhaps seeking to salve his conscience for having sent no aid to the Texas colony since his return to France-concerning the possibility that survivors of La Salle's settlement might remain alive among the natives. Iberville, replying on May 3, 1704, enclosed an extract of the Talon children's answers to interrogations, assuring the cleric that every effort had been made to find any remaining Frenchmen without success. Cavelier died not long afterward.