The Rev. James E. Orange of Birmingham, Ala., died on Saturday at Crawford Long Hospital. He was 65.
"Today, Reverend Orange's courageous spirit and commitment to justice lives on in all of us who believe that change is possible," said Sen. Barack Obama, D-Ill. "Michelle and I send our deepest sympathies to his wife and family. His legacy will never be forgotten.
"As a trailblazer of the Civil Rights Movement, Reverend Orange was instrumental in mobilizing thousands of young people to participate in voter registration drives and marches in Alabama and throughout the South," Mr. Obama added.
"We are all weaker today because James Orange is no longer with us," said Edward Dubose, the president of the Georgia NAACP. "We have lost a great soldier in the struggle for freedom and equality."
The Rev. Orange's daughter, Jamida Orange, told The Atlanta Journal-Constitution he was admitted to the hospital for gallbladder surgery. She said he had complications and was scheduled for follow-up tests Saturday when he died.
"I'm stunned," Ms. Orange said. "Not only did I lose my parent, but I lost an actual role model, and a lot of the people in the country lost a role model."
The Rev. Orange marched in his hometown in 1963 alongside Dr. King and the Rev. Ralph David Abernathy. He lived in southwest Atlanta for more than four decades.
As project coordinator with the SCLC from 1965 to 1970, the Rev. Orange later became a regional coordinator with the AFL-CIO in Atlanta, where he incorporated Dr. King's nonviolence philosophy and promoted unity between national labor leaders and Dr. King's "beloved community." He retired in 2005.
Since 1995, the Rev. Orange served as the general coordinator of the Martin Luther King Jr. March Committee-Africa/African-American Renaissance Committee. The organization coordinates the country's most watched and heavily attended events of the King national holiday. It also promoted trade between Atlanta and the U.S. with South Africa.
The Rev. Orange is survived by his wife, Cleo; five children and two grandchildren.
Funeral arrangements had not been announced Sunday.