Louis Juchereau de St. Denis, the eleventh of twelve children of Nicolas Juchereau and Marie Thérèse Giffard, was born near Quebec on September 17, 1674. It appears that his parents were able to send him to France for further education. In late 1699, St. Denis sailed from La Rochelle to Louisiana on the second expedition of Pierre Le Moyne, Sieur d'Iberville, his relative by marriage. In Louisiana St. Denis commanded a fort on the Mississippi River and another at Biloxi Bay. He also carried out important explorations to the west of the bay and upstream, where he ascended the lower Red River. These journeys brought him into contact with Karankawa and Caddo Indians and taught him invaluable lessons on how to cope in wilderness areas. In response to a letter received from Father Francisco Hidalgo, the French governor of Louisiana, Antoine de La Mothe, Sieur de Cadillac, dispatched St. Denis and a company of men from Mobile in September 1713. The Canadian-born adventurer reached the Natchitoches villages in that same year and left some of his goods for safekeeping. From Natchitoches he traveled to lands of the Hasinai Indians and thence to Spanish outposts on the Rio Grande. At San Juan Bautista, Commander Diego Ramón placed St. Denis under a pleasant house arrest while awaiting instructions from Mexico City on what to do with an foreigner bearing goods banned by Spanish mercantile restrictions. In the interim, the Frenchman used the occasion to court and win a promise of marriage from Ramón's beautiful granddaughter, Manuela Sánchez (see ST. DENIS, MANUELA S. N. DE). After being ordered to Mexico City, St. Denis defended himself ably and was appointed as commissary officer of the Ramón expedition, charged with founding Spanish missions in East Texas.
After returning to San Juan Bautista, St. Denis married Manuela, probably in early 1716, and he subsequently participated in the founding of six missions and a presidio in East Texas during the years 1716–17. In April 1717 he returned to San Juan Bautista with a sizable amount of merchandise. But whereas he had been well received on his first visit, the death of Louis XIV and the conclusion of the War of the Spanish Succession had ended the era of Franco-Spanish cooperation. When sent to Mexico City for a second time, St. Denis fled the capital to avoid being hauled to Spain as a prisoner. He made his way to Natchitoches by February 1719. In 1721 Spanish officials permitted his wife to join him, and the couple spent their remaining years at the French outpost on the Red River. From his command at Natchitoches, St. Denis was often a troublesome thorn for Spanish Texas. Controversy continues to surround his motives and actions. He insisted that his marriage to Manuela Sánchez indicated a desire to become a Spanish subject; suspicious Spaniards, however, saw him as a covert agent of France. His accomplishments are indisputable: St. Denis contributed to the expanded geographical knowledge of both France and Spain, brought Spanish and French settlements into close proximity, and made contraband trade a way of life on the borders of Spanish Texas and French Louisiana. On January 10, 1743, he wrote to Jean Frédéric Phélypeaux, Comte de Maurepas, at Versailles indicating that he could no longer perform his duties as commandant of Natchitoches. He also asked permission to retire to New Spain with his wife and children. That request was denied. St. Denis died at Natchitoches on June 11, 1744. He was survived by his wife and four or five children, one of whom was married briefly to Athanase de Mézières.