Derrick A. Bell Jr., a onetime civil rights lawyer whose provocative ideas about race and the law made him one of the country’s most influential legal thinkers and led to his dismissal from the faculty of Harvard Law School, died Oct. 5 of cancer in New York City. He was 80.

New York University Law School, with which Mr. Bell had been associated since 1990, announced his death.

In 1971, Mr. Bell became the first African American faculty member to gain tenure at Harvard Law School. He was one of the school’s most popular professors, regularly received prestigious grants and, in 1973, published “Race, Racism and American Law,” which has gone through several editions and has become a standard text in law schools.

Mr. Bell was credited with developing “critical race theory,” which suggested that the U.S. legal system was inherently biased against African Americans and other minorities because it was built on an ingrained white point of view. He argued in his many books and lectures that the life experiences of black people and other minorities should be considered in hiring decision and in applying the law.

Early in his career, Mr. Bell worked for the NAACP Legal Defense and Educational Fund, managing hundreds of school desegregation cases in Mississippi. He spent a night in jail when he refused to leave a railroad waiting room reserved for whites.

In the early 1960s, he was a legal adviser in the effort to enroll James Meredith, an African American student, in the previously all-white University of Mississippi. After violent white resistance, federal marshals helped escort Meredith to class in 1962.

Later, while working for the civil rights office of the old Department of Health, Education and Welfare, Mr. Bell helped enforce provisions of the Civil Rights Act of 1964.

Several times throughout his career, Mr. Bell resigned his positions over what he considered matters of principle. In 1959, when his bosses at the Justice Department told him it was a conflict of interest for him to belong to the NAACP, Mr. Bell quit his job.

He threatened to leave Harvard before he was granted tenure. After becoming dean of the law school at the University of Oregon in 1980, he resigned five years later when the school would not hire two Asian American women for its faculty.

Mr. Bell maintained that the standards for promotion and tenure at law schools — and Harvard, in particular — were inherently discriminatory and excluded a broad group of minorities. By hiring only graduates of top-tier law schools who had clerked at the Supreme Court, he argued, academia was populated by a uniform group of standard-issue professors, most of them white men.

Mr. Bell said the schools should give equal weight to the life experiences and racial makeup of people from other backgrounds.

He put his theory into practice in 1990, four years after he had returned to Harvard from his sojourn in Oregon. At that time, Harvard Law School had 60 tenured faculty members, including five who were women and three who were black.

Demanding that the law school give tenure to a “woman of color,” Mr. Bell took an unpaid leave of absence as an act of protest, forgoing his annual salary of $120,000.

“I cannot continue to urge students to take risks for what they believe if I do not practice my own precepts,” he said at the time.

When one professor told him, “This is a university, not a lunch counter in the Deep South,” Mr. Bell’s resolve was only strengthened.

“It is simply crazy, wrong and insulting to say that none of the people in the small pool of black women professors are qualified to teach at Harvard,” he told The Washington Post.

Mr. Bell had the support of many of his students and some faculty members, but his stance proved to be deeply divisive. One veteran faculty member called him “off his head,” and another said, “It’s more important to maintain Harvard’s standards of excellence than to improve the diversity of the faculty.”

Conservative commentators viewed Mr. Bell’s academic dispute as an act of arrogant self-entitlement. Political scientist Abigail Thernstrom, writing in the conservative journal National Review, said he was “lost in a world of his own making — one in which paranoid delusions obscure the most obvious facts.”

Syndicated columnist George F. Will wrote, “This entitlement mentality causes blacks to cultivate the attitudes of victims, triggers in whites the instinct of condescension and leads both to discount black achievements.”

After two years, Harvard interpreted Mr. Bell’s absence as a formal resignation and stripped him of his tenure. By then, he was already teaching at NYU. In 1998, Lani Guinier became the first African American woman to receive tenure at Harvard Law School.

Derrick Albert Bell Jr. was born Nov. 6, 1930, in Pittsburgh to parents who had come north from Alabama. His father had a trash-hauling business.

Mr. Bell graduated in 1952 from Duquesne University in his hometown and served in the Air Force during the Korean War. In 1957, he received a law degree from the University of Pittsburgh, where he was the only black member of his class.

His first wife, Jewel Hairston Bell, died in 1990.

Survivors include his wife of 19 years, Janet Dewart Bell of New York; three sons from his first marriage, Derrick A. Bell III and Douglass Dubois Bell, both of Pittsburgh, and Carter Robeson Bell of New York; two sisters; and a brother.

In the 1980s, Mr. Bell began to introduce elements of fable and allegory to his legal writing. He used a fictional civil rights lawyer named Geneva Crenshaw to illustrate various points of law. He wrote two autobiographical volumes and a 2004 book, “Silent Covenants,” analyzing the long-term effects of the 1954 Brown v. Board of Education decision, which desegregated public schools in the United States.

Mr. Bell became a sharp critic of efforts to bring about racial reconciliation after the civil rights era and said black Americans faced more discrimination in the 1990s than they had since the days of slavery.

“Black people will never gain full equality in this country,” he wrote in his 1992 book “Faces at the Bottom of the Well: The Permanence of Racism.”

“Even those herculean efforts we hail as successful will produce no more than temporary ‘peaks of progress,’ short-lived victories that slide into irrelevance as racial patterns adapt in ways that maintain white dominance.”

Some scholars, both black and white, challenged Mr. Bell’s ideas, as well as his strong support of Nation of Islam leader Louis Farrakhan. Nonetheless, Mr. Bell remained one of the country’s most outspoken public intellectuals until his death.

“All through my life,” he told Boston Globe in 1992, “I’ve known confrontation makes history, that nothing gets done without pushing.”