SNCC had undertaken an ambitious voter registration program in Selma, Alabama, in 1963, but by 1965 little headway had been made in the face of opposition from Selma's sheriff, Jim Clark. After local residents asked the SCLC for assistance, King came to Selma to lead several marches, at which he was arrested along with 250 other demonstrators. The marchers continued to meet violent resistance from the police. Jimmie Lee Jackson, a resident of nearby Marion, was killed by police at a later march on February 17, 1965. Jackson's death prompted James Bevel, director of the Selma Movement, to initiate and organize a plan to march from Selma to Montgomery, the state capital.

On March 7, 1965, acting on Bevel's plan, Hosea Williams of the SCLC and John Lewis of SNCC led a march of 600 people to walk the 54 miles (87 km) from Selma to the state capital in Montgomery. Six blocks into the march, at the Edmund Pettus Bridge where the marchers left the city and moved into the county, state troopers, and local county law enforcement, some mounted on horseback, attacked the peaceful demonstrators with billy clubs, tear gas, rubber tubes wrapped in barbed wire, and bullwhips. They drove the marchers back into Selma. Lewis was knocked unconscious and dragged to safety. At least 16 other marchers were hospitalized. Among those gassed and beaten was Amelia Boynton Robinson, who was at the center of civil rights activity at the time.

The national broadcast of the news footage of lawmen attacking unresisting marchers seeking to exercise their constitutional right to vote provoked a national response and hundreds of people from all over the country came for a second march. These marchers were turned around by King at the last minute so as not to violate a federal injunction. This displeased many demonstrators, especially those who resented King's nonviolence.

That night, local Whites attacked James Reeb, a voting rights supporter. He died of his injuries in a Birmingham hospital on March 11. Due to the national outcry at a White minister being murdered so brazenly, the marchers were able to lift the injunction and obtain protection from federal troops, permitting them to make the march across Alabama without incident two weeks later; during the march, Gorman, Williams, and other more militant protesters carried bricks and sticks of their own.