The spiritualist movement that emerged in Europe and the United States in the 19th century held that humans could communicate with the spirits of those who had departed the earthly realm. It posited parallels between the earthly plane and that of the spirit world where the human spirit would dwell and continue to evolve toward perfection following bodily death.

Partly based on the writings of Swedish mystic Emanuel Swedenborg, spiritualism's beliefs and practices affirmed not only the continued existence of the human soul after physical death but also the possibility of communication between the living and the departed. Swedenborg said there were levels or planes of existence through which the spirits traveled as they continued their evolution toward perfection. Moreover, the spirits acted as intermediaries between God and humanity, and could therefore act as moral guides. Seances, table-turning, and spirit-writing practices were common methods individuals or sensitive "mediums" used to contacted spirits which then imparted information about the afterlife. The term "spiritualism" came to include a range of metaphysical arts such as mesmerism (hypnotism) and phrenology.

Spiritualism became popular in the United States following the 1847 publication of the book The Principles of Nature, Her Divine Revelations, and a Voice to Mankind, by Andrew Jackson Davis of Poughkeepsie, New York. Davis claimed to have received the book's content from the spirit of Emanuel Swedenborg while in a trance. When, in the following year, the Fox sisters of Rochester, New York, made contact with the spirit of a deceased peddler through audible rappings, they and spiritualism became a sensation.

At its peak in the United States, spiritualism was estimated to have eight million followers. So although its optimistic beliefs were a natural fit for both Unitarianism and Universalism, spiritualism as a religion far outstripped either in numbers of followers.

In the idealistic, romantic atmosphere of the 19th century, spiritualism was seen as scientific proof that the human soul not only continues after death, but continues to grow and improve. This idea offered comfort to the bereaved and gave credence to the idea of universal salvation. Many Universalist ministers and parishioners espoused spiritualism and practiced its arts. Universalist ministers Adin Ballou, John Spear, Joshua Ingalls, and Linus Smith were all adherents as were former ministers Samuel Brittan, William Fishbough, and James Peebles. One of the most popular trance lecturers was the much-married Cora L. V. Scott Hatch Daniels Tappan Richmond whose family had been members of Adin Ballou's Hopedale Community.

Spiritualism also spoke to Unitarians, as evidence of their belief in the continual upward progress of humankind, and, since it was purported to be scientifically based, appealed to rationality and the contemporary belief that science could reveal all truths. Reinforced by Transcendentalism's penchant for mystical experience, spiritualism became favored by many radical Unitarians. Ministers John Pierpont, Theodore Higginson, Allen Putnam, and Herman Snow openly embraced spiritualism while others like William Henry Channing and Theodore Parker acknowledged its benefits but never publicly associated with the movement.

Although books were published on its philosophy and practices, and more than three dozen spiritualist periodicals were in circulation worldwide by the 1880s, 19th-century spiritualism never institutionalized into a religious denomination. Nevertheles, it was practiced widely in the public sphere. Mediums and mesmerists filled large auditoriums with people seeking evidence of life beyond life through communication from spirits.

While many Universalists and Unitarians embraced spiritualism, their numbers also included many detractors. Universalist clergy such as Thomas Whittemore, Thomas Sawyer, and Hosea Ballou 2nd spoke against it. On the Unitarian side, Ralph Waldo Emerson described spiritualism as "midnight fumblings over mahogany," referencing the table-rappings of the spirits. Some supporters turned against spiritualism as mediums and practices were increasingly exposed as fraudulent.

Beginning in the 1920s, interest in spiritualism decreased though remnants of the movement may still be found in the Spiritualist Church and New Age movements.