Unitarian Universalists have historically been closely involved with civil rights and social justice movements. John Haynes Holmes, a UU minister, was among the founders of both the NAACP and the ACLU, chairing the latter for a time. Approximately 20% of Unitarian Universalist ministers marched with Martin Luther King, Jr., from Selma, Alabama, to Montgomery. UU ministers have been performing same-sex unions since at least the late 1960s.

In 1995 the UUA helped establish the International Council of Unitarians and Universalists (ICUU).