The cause was a stroke, according to a spokesperson for the University of Southern California’s Viterbi School of Engineering. Dr. Slaughter taught at the school for more than a decade, with a joint appointment at the USC Rossier School of Education, before retiring last summer.

A respected engineer and administrator with an impish sense of humor, Dr. Slaughter was one of the first three African Americans inducted in the National Academy of Engineering, and was among the most prominent Black leaders in higher education. He was perhaps best known for spending more than half a century working to improve educational opportunities for women and students of color, while also emphasizing the importance of broad training in science and the humanities.

“I tell students they need to study both Bach and botany, both Carlyle and chemistry, both Dickinson and differential equations,” he said.

Raised in racially segregated Topeka, Kan., Dr. Slaughter graduated from high school shortly before local Black families filed the lawsuit that became Brown v. Board of Education. He had few Black role models in his field when he launched his engineering career at General Dynamics in 1956 — he liked to say he was the first Black engineer he ever met — and went on to develop military computer systems while spending 15 years at the Navy Electronics Laboratory in San Diego.

But he found that he “enjoyed working with people more than things,” as he put it, and served as an assistant director at the National Science Foundation and as provost at Washington State University before President Jimmy Carter appointed him to run the NSF in 1980.

As director of the independent agency, Dr. Slaughter promoted educational programs in science and helped allocate hundreds of millions of dollars in basic-research funding. But he was dismayed by budget cuts during the Reagan administration and left the job in 1982, with four years left in his term, to become chancellor of the University of Maryland at College Park, the flagship campus of the state university system.

He spent the next six years working to increase the school’s profile, burnish its academic reputation and diversify the ranks of faculty and students — no small task at a university that began admitting Black undergraduates only 30 years earlier.

“Through talent and likability, John was able to make us understand the dual goals of excellence and equity, and how compatible and important they were,” William “Brit” Kirwan, who served as provost under Dr. Slaughter and succeeded him as the school’s top official, said in a 1999 interview with the Los Angeles Times.

As chancellor (the position was renamed president after he left office), Dr. Slaughter was credited with expanding minority faculty hiring, developing science and technology programs, and heightening admissions standards. He also steered the university through controversy in 1986, when basketball star Len Bias ingested a fatal dose of cocaine in his dormitory suite and died two days after being selected as the second overall pick in the NBA Draft.

Bias’s death prompted soul-searching on campus, where a university investigation uncovered widespread academic problems among student-athletes. Athletic director Dick Dull resigned, and the school’s popular basketball coach, Lefty Driesell, was forced from his job after months of speculation. Critics called for Dr. Slaughter to be ousted as well, arguing that his deliberate and methodical approach to the crisis only prolonged a traumatic period that threatened to overshadow the school’s successes.

Dr. Slaughter said that he should have been more aware of what was happening in the athletic department, and presided over rule changes that included a new minimum grade-point average for student-athletes. In a tribute after his death, the university praised the “characteristic integrity and steadiness” with which he guided the school “through one of the most tumultuous periods in its history.”

To Dr. Slaughter, college sports was “just a business,” as he later put it in a Times interview, one in which student-athletes were too often exploited. Clashes over the Maryland athletics program, as well as a debate in the state legislature over expanding and overhauling Maryland’s public university system, reportedly contributed to his decision to resign in 1988, when he left College Park to become president at a far smaller school, Occidental College.

The private liberal arts school had 1,600 students, in contrast to 38,000 at College Park, and less emphasis on sports, competing in Division III of the NCAA. Its student body was overwhelmingly White.

By the time Dr. Slaughter retired in 1999, 43 percent of Occidental’s students were Asian, Latino or Black, and more than half of the faculty hired in the previous decade were women, people of color or both. The school received a record number of applicants during his tenure, and Occidental students received high-profile awards, including the college’s first Rhodes scholarships in 27 years.

“Quality and equality are inseparable,” Dr. Slaughter had said when he was inaugurated as president, “and diversity is synonymous with what is best in America.”

The oldest of four children, he was born in Topeka on March 16, 1934. His mother was a homemaker, and his father sold used furniture and worked as a janitor.

Growing up, Dr. Slaughter pored over the pages of magazines like Popular Science and Popular Mechanics and would repeatedly take apart and reassemble his bicycle, studying how the pieces fit together. But when he told a school guidance counselor he wanted to be an engineer, he was placed in a vocational program and encouraged to plan for a career as a radio repairman.

Lacking the math and science courses he needed for a college engineering degree, he spent two years at what is now Washburn University in Topeka. Dr. Slaughter said he was the only Black engineering student in his class when he graduated from Kansas State College of Agriculture and Applied Science, now Kansas State University, in 1956.

That same year, he married Ida Bernice Johnson. She survives him, along with two children, Johnny Slaughter Jr. and Jacqueline Michelle Randall; and a sister.

Dr. Slaughter received a master’s degree in engineering from UCLA in 1961 and a doctorate in engineering science from the University of California at San Diego in 1971. He led the Applied Physics Laboratory at the University of Washington before joining the NSF for the first time, in 1977, as assistant director of astronomical, atmospheric, earth and ocean sciences.

While working in higher education, he served on the board of companies including IBM and Northrop Grumman. He was also appointed to civic groups including the Christopher Commission, formed by Los Angeles Mayor Tom Bradley to examine the city’s police department after Rodney King, a Black motorist, was filmed being beaten by LAPD officers in 1991.

After retiring from Occidental, Dr. Slaughter was chief executive of the National Action Council for Minorities in Engineering. He also turned to teaching, joining the faculty at USC in 2010. He was honored at the White House in 2015 with the Presidential Award for Excellence in Science, Mathematics and Engineering Mentoring, and in September USC’s Center for Engineering Diversity — where Dr. Slaughter would casually join students for lunch — was renamed in his honor.

“To have the center named after me,” he said, “is greater than any honor I’ve ever received.”