In 1960, Harding and his wife, Rosemarie Freeney Harding, moved to Atlanta, Georgia, to participate in the Southern Freedom Movement as representatives of the Mennonite Church. The Hardings co-founded Mennonite House, an interracial voluntary service center and movement gathering place in Atlanta. The couple traveled throughout the South in the early 1960s working as reconcilers, counselors and participants in the Movement, assisting the anti-segregation campaigns of the Southern Christian Leadership Conference (SCLC), the Student Nonviolent Coordinating Committee (SNCC) and the Congress of Racial Equality (CORE). Vincent Harding occasionally drafted speeches for Martin Luther King Jr., including King's famous anti-Vietnam speech, "A Time to Break Silence", which King delivered on April 4, 1967, at Riverside Church in New York City, exactly a year before he was assassinated.