A native of Belgium, De Smet came to the United States in 1821 at the age of 20. He became a novitiate of the Jesuit order in Maryland and was subsequently ordained in St. Louis. As a priest, De Smet's ambition was to be a missionary to the Native Americans of the Far West. In 1838, he was sent to proselytize among the Potawatomi villages near today's Council Bluffs, Iowa. There, he met a delegation of Flathead Indians who had come east seeking a "black robe" whom they hoped might be able to bring the power of the Christian god to aid their tribe. During the 1840s, De Smet made several trips to work with the Flathead in present-day western Montana. He established a thriving mission and eventually secured a peace treaty with the Flathead's previously irreconcilable enemy, the Blackfeet.
A genuine friend to the Native Americans, De Smet earned a reputation as a white man who could be trusted to fairly negotiate disputes between Indians and the American government. During the 1860s, such disputes became increasingly common in the West, where Plains Indians like the Sioux and Cheyenne resisted the growing flood of white settlers invading their territories. The U.S. government began to demand that all the Plains Indians relocate to reservations. Leaders in the American government and military hoped the relocation could be achieved through negotiations, but they were also perfectly willing to use violence to force the Indians to comply.
One of the principal leaders of the so-called "hostile" Indians that resisted relocation was the great Chief of the Teton Sioux, Sitting Bull. In May 1868, the federal government asked De Smet to meet with Sitting Bull to negotiate a peace treaty. The 67-year-old De Smet agreed to try, and on this day in 1868, he met with Sitting Bull at his camp along the Powder River in present-day Montana.
Although tensions were high, Sitting Bull had promised to meet De Smet with "arms stretched out, ready to embrace him." Lest any hotheaded young brave do something foolish, Sitting Bull first talked with De Smet in his own lodge in order to ensure the priest's safety. The next day, De Smet met with a council that included other chiefs. De Smet was not able to convince Sitting Bull personally to sign a peace treaty. However, the chief did agree to send one of his lesser chiefs to Fort Laramie, Wyoming, to sign a treaty in which the Sioux agreed to allow white travel and settlement in specified areas.
Although Sitting Bull himself had not agreed to the treaty, the negotiations were a triumph for De Smet. As one historian later noted, "No White Man has ever come close to equaling his universal appeal to the Indian." De Smet spent the remaining five years of his life continuing to work for peace with the Plains Indians. Through his books and speaking tours, he also attempted to bring a sympathetic portrait of the Indians to an American public that tended to think of Indians as bloodthirsty savages. Ultimately, however, De Smet was unable to stop the tragic Plains Indian War that eventually forced Sitting Bull and other Indians to leave their homes and move to government-controlled reservations.
De Smet died in St. Louis in 1873, three years before Sitting Bull won his greatest victory in his war with the United States at the Battle of the Little Big Horn.