He was assassinated in Keener, Alabama, during a protest march from Chattanooga, Tennessee to Jackson, Mississippi, where he intended to deliver a letter to Governor Ross Barnett, supporting civil rights.

In the early 1960s, he undertook three civil rights protests in which he marched to a capital to hand-deliver letters he had written denouncing racial segregation.

For his third protest he planned to walk from Chattanooga, Tennessee to Jackson, Mississippi and deliver a letter to Governor Ross Barnett urging him to accept integration.

On April 23, 1963, about 70 miles (110 km) into his march, Moore was interviewed by Charlie Hicks, a reporter from radio station WGAD in Gadsden, Alabama, along a rural stretch of U.S. Highway 11 near Attalla.

Less than an hour after the reporter left the scene, a passing motorist found Moore's body about a mile farther down the road, shot twice in the head at close range with a .22 caliber rifle.

He asked Governor Barnett to: "Be gracious and give more than is immediately demanded of you...." Folk singer Phil Ochs wrote a song in tribute to William Moore that is part of the posthumously released 1986 album A Toast to Those Who Are Gone.

[5] Bob Zellner, a long time activist and first white Field Secretary of the Student Non-Violent Coordinating Committee, was with them and attempted to present the letter to Governor Haley Barbour on May 6, 2008, but the latter declined to meet with the party.

Grant arranged for Smith to speak to the commission, and members committed to giving money from their discretionary funds to pay for the marker.