Black Elk married his first wife, Katie War Bonnett, in 1892. She became a Catholic, and all three of their children were baptized as Catholic. After her death in 1903, he too became baptized, taking the name Nicholas Black Elk, and continued to serve as a spiritual leader among his people, seeing no contradiction in embracing what he found valid in both his tribal traditions concerning Wakan Tanka (The Great Spirit), and those of Christianity.

Black Elk met the poet John Neihardt in 1930, a meeting that resulted in the book Black Elk Speaks (1932). Black Elk dictated his autobiography to Neihardt and recounted Lakota history and traditions in an effort to preserve them. In 1947, Joseph Epes Brown met Black Elk in Nebraska. Brown spent the next winter with the elderly spiritual teacher in Manderson, South Dakota. Through that contact and their conversations, Black Elk provided the details of seven traditional rituals of the Oglala people which Brown published as The Sacred Pipe. The rites described included the purification ceremony (the sweat lodge), crying for a vision, female puberty, marriage, soul-keeping, throwing the ball, and the greatest medicine of all traditional Plains people, the Sun Dance.

The new edition of Brown's other classic book, The Spiritual Legacy of the American Indian, contains previously unpublished correspondence from Brown during his time on the reservation, which sheds new light on the debate on whether Black Elk was indeed a sincere Catholic, as well as recording many of Black Elk’s observations on modern ways and traditional Indian spiritual values. Another World Wisdom book, Indian Spirit, contains numerous excerpts of Black Elk's words taken from various sources.