Through the relentless struggles of the Civil Rights Movement, Julian Bond always kept his sense of humor. His steady demeanor helped him persist despite the inevitable difficulties involved, his wife recalled.

Mr. Bond “never took his eyes off the prize — and that was always racial equality,” his wife, Pamela Horowitz, said Sunday.

“He always ... in that hard struggle kept a sense of humor, and I think that’s what allowed him to do that work for so long — his whole life really,” his wife added.

Mr. Bond died Saturday, Aug. 15, 2015, in Fort Walton Beach, Fla., his wife said. He was 75. Ms. Horowitz said she did not yet know the exact cause of death, but that her husband had circulatory problems.

Mr. Bond’s life traced the arc of the Civil Rights Movement, from his efforts as a young man to start a student protest group, through a long career in politics and his leadership of the NAACP almost four decades later.

Year after year, the calm, telegenic Mr. Bond was one of the nation’s most poetic voices for equality, inspiring fellow activists with his words in the 1960s and sharing the movement’s vision with succeeding generations as a speaker and academic.

“Julian Bond was a hero and, I’m privileged to say, a friend,” President Obama declared in a statement. “Justice and equality was the mission that spanned his life — from his leadership of the Student Nonviolent Coordinating Committee, to his founding role with the Southern Poverty Law Center, to his pioneering service in the Georgia legislature and his steady hand at the helm of the NAACP.

“Julian Bond helped change this country for the better. And what better way to be remembered than that,” the president added.

Former U.N. Ambassador Andrew Young said Mr. Bond’s legacy would be as a “lifetime struggler.”

“He started when he was about 17 and he went to 75,” Mr. Young said. “And I don’t know a single time when he was not involved in some phase of the Civil Rights Movement.”

Mr. Bond’s death was first announced by the Southern Poverty Law Center, an advocacy group he founded in 1971 and helped oversee for the rest of his life.

Morris Dees, co-founder of the law center, said the nation had lost one of its most passionate voices for justice.

“He advocated not just for African-Americans but for every group, indeed every person subject to oppression and discrimination, because he recognized the common humanity in us all,” Mr. Dees said.

The son of a college president, Mr. Bond was born Jan. 14, 1940, in Nashville, Tenn. He burst into the national consciousness after helping to start the Student Non-Violent Coordinating Committee, where he rubbed shoulders with committee leaders Stokely Carmichael and John Lewis.

As the committee grew into one of the movement’s most important groups, the young Mr. Bond dropped out of Morehouse College in Atlanta to serve as SNCC communications director. He later returned and completed his degree in 1971.

Mr. Bond was elected to the Georgia House of Representatives in 1965, but fellow lawmakers, many of them white, refused to let him take his seat because of his anti-war stance on Vietnam. The case went all the way to the U.S. Supreme Court, which ruled in his favor. Mr. Bond finally took office in 1967.

“If this was another movement, they would call him the PR man, because he was the one who wrote the best, who framed the issues the best. He was called upon time and again to write it, to express it,” said Eleanor Holmes Norton, who was Mr. Bond’s colleague at SNCC and later wrote a friend-of-the-court brief for the American Civil Liberties Union when Mr. Bond’s case was before the high court.

In 1968, Mr. Bond led a delegation to the Democratic National Convention, where his name was placed in nomination for the vice presidency, but he declined because he was too young.

He served in the Georgia House until 1975 and then served six terms in the Georgia Senate until 1986. He also served as president of the law center from its founding until 1979 and was later on its board of directors.

Mr. Bond was elected board chairman of the NAACP in 1998 and served for 10 years.

He was known for his intellect and his even keel, even in the most emotional situations, Mr. Young said.

“When everybody else was getting worked up, I could find in Julian a cool serious analysis of what was going on,” he said.

Mr. Bond was often at the forefront of protests against segregation. In 1960, he helped organize a sit-in involving Atlanta college students at the city hall cafeteria.

“We never thought that he really would participate and be arrested because he was always so laid back and cool, but he joined in with us,” recalled Carolyn Long Banks, now 74, who said Mr. Bond never sought much recognition in those early years.

After leading the NAACP, Mr. Bond stayed active in Democratic politics. He also made regular appearances on the lecture circuit and on television and taught at several universities, including the University of Virginia in Charlottesville, where he served on the history department faculty for 20 years until his retirement in 2012.

“It was a tremendous opportunity for our students to be taught by a living legend like Mr. Bond,” said George Keith Martin of Richmond, immediate past rector of the university. “I am pleased that the university will endow the Julian Bond Professorship in Civil Rights and Social Justice in his honor.”

King Salim Khalfani, former executive director of the Virginia State Conference NAACP, remembers Mr. Bond as a mentor, icon and co-worker who often invited him to Charlottesville to hear lectures presented by Mr. Bond and guest lecturers such as Vernon Jordan.

“He was brilliant. His analysis and assessment of the issues we faced were sharper than a knife,” Mr. Khalfani said. “He was always willing and able to assist the (Virginia NAACP) to address the issues we faced right here in the Commonwealth.”

Mr. Bond is survived by Ms. Horowitz and five children. Funeral plans have not been finalized, but Ms. Horowitz said her husband will be cremated and his ashes scattered over the Gulf of Mexico.