What is now known as Unitarian Universalism came into being in 1961 when two previously independent but friendly denominations, the American Unitarian Association and the Universalist Church of America, merged to become the Unitarian Universalist Association.

Unitarianism in the United States became a distinct movement in the early part of the nineteenth century as a rejection of the rigidly dogmatic Calvinism which was then dominant. The Unitarians, led by such notables as William Ellery Channing, challenged the logic and plausibility of some of the key Calvinist doctrines, insisting on the full humanity of Jesus and the loving-kindness of God. Universalism had an earlier origin, being founded in the late eighteenth century, and having as its core principle the belief that no loving God would consign anyone to eternal torment but that salvation was universally available. Early Unitarians and Universalists understood themselves as part of the Christian church, though other dogmatic Christians condemned and ostracized them.

From the beginning of both traditions, the primacy of individual conscience in matters of faith has been a central tenet. This lack of doctrinal conformity has led to the welcoming of other types of thought. In the late nineteenth century, the scientific insights of Darwin were incorporated rather than resisted (not entirely surprising, as Darwin himself was a Unitarian). In the early twentieth century, Unitarian ministers were among the first signatories of the Humanist Manifesto. The theological insistence on the worth and dignity of all persons has placed Unitarian Universalists at the forefront of feminism, the struggle for LGBT equality, anti-racism and anti-imperialism.

In 1984, after several years of deliberative consultation, the Unitarian Universalist Association adopted its statement of Seven Principles. Member congregations of the UUA covenant (promise each other) to affirm and promote:

  1. The inherent worth and dignity of every person;
  2. Justice, equity and compassion in human relations;
  3. Acceptance of one another and encouragement to spiritual growth in our congregations;
  4. A free and responsible search for truth and meaning;
  5. The right of conscience and the use of the democratic process within our congregations and in society at large;
  6. The goal of world community with peace, liberty, and justice for all;
  7. Respect for the interdependent web of all existence of which we are a part.