The death was announced in a family statement. No cause was given.

For decades, Mr. Lewis wielded influence in roles such as adviser to D.C. Mayor Marion Barry and as chief executive at the former Chesapeake & Potomac Telephone Company (then part of Bell Atlantic) from 1990 to 1993. Mostly, however, he remained out of the headlines.

That changed when he took over at NPR in 1993, succeeding a former Carter administration official, Douglas Bennet, who had guided the broadcaster from the wake of a debt crisis in 1983 to relative stability at the dawn of the internet age. Mr. Lewis was soon facing another siege on NPR.

Republicans — emboldened after gaining control of the House and Senate in 1994 — took aim at taxpayer help for NPR, which received funding through the nonprofit Corporation for Public Broadcasting. For firebrands such as House Speaker Rep. Newt Gingrich (R-Ga.), calls to defund NPR became early salvos in the political culture wars, claiming NPR was not attuned to conservative views and values.

Mr. Lewis was thrust onto the front lines. He mobilized NPR’s hundreds of affiliates across the country to lobby local representatives and senators to keep funding. Mr. Lewis, who was educated in segregated schools in Kansas and was NPR’s first Black chief executive, portrayed Gingrich and his allies as trying to cripple affiliate stations with minority ownership or serving rural areas without easy access to cultural offerings.

“It is on public radio that people hear public discourse in more than 15-second sound bites,” Mr. Lewis wrote in a February 1995 opinion piece in The Washington Post. “It is on public radio that people in rural areas hear a live performance of a major symphony orchestra. It is on public radio that reading services for the blind are found.”

In the end, critics of NPR funding retreated. But the broadcaster’s budget took a hit: $275 million for 1996, down from $425 million the previous year. Mr. Lewis dropped some of the very same programs he praised during the fight with Congress — music shows including “Afropop Worldwide” and “BluesStage.”

“It’s not an easy time,” Mr. Lewis told the New York Times.

The belt-tightening left the NPR newsroom uneasy about what could come next. Discontent grew as Mr. Lewis began to sketch out financial rescue strategies, including proposing more direct corporate sponsorship of NPR and making a failed pitch to merge with a rival, Public Radio International. “Diversity’s color,” Mr. Lewis once said, “is green.”

The tensions stoked by Mr. Lewis metastasized into open hostility by newsroom leaders such as the vice president for news, Bill Buzenberg, who believed Mr. Lewis and his management team “didn’t fully grasp the mission of public-service journalism or the business of public radio,” wrote Michael McCauley in his 2005 book “NPR: The Trials and Triumphs of National Public Radio.”

Yet Mr. Lewis, who stepped down from NPR in 1998, also recognized the changing media landscape before many others. He saw how the internet would change traditional media and open new opportunities as well as threats. In a 1994 interview, he envisioned a then-futuristic world of podcasts and smartphones.

“As this information infrastructure develops, it is key for radio to be involved,” he told Broadcasting & Cable magazine. “The way we shop, bank, entertain, receive news and educate our children will all change. Technology is exploding.”

As his farewell approached at NPR, Mr. Lewis vowed that his overall work life was winding down, too. “I’m going to pursue fun things in life,” he told NPR staff. But a few months later, as Mr. Lewis and his wife, Gayle, were packing to move to Las Cruces, the phone rang. It was Vice President Al Gore.

“He says, ‘Del, this is Al,’ ” Lewis wrote in his memoir, “No Condition Is Permanent” (2018), co-written with his son Brian. “Then his voice turned very official and he continued, ‘Del, I am calling on behalf of President Clinton and the president would like to nominate you as the next ambassador to the Republic of South Africa.’ ”

The posting put Mr. Lewis in a country making a difficult political transition. The hero of the anti-apartheid struggle, Nelson Mandela, left the presidency in June 1999. His successor, Thabo Mbeki, quickly unleashed a more confrontational style with the United States and allies. A major break with the West came when Mbeki questioned the scientific evidence that HIV caused AIDS, which at the time was ravaging sub-Saharan Africa.

Mr. Lewis was in the middle: urging Mbeki to work with U.S. and Western researchers to combat HIV transmission, while advising the State Department on how to deal with South Africa’s mercurial leader. “The challenge for U.S. officials,” Mr. Lewis wrote in a cable in February 2001, less than four months before leaving the ambassador post, “will be to accept this important, but hypersensitive, African figure as he is, and build a constructive dialogue.” (Mbeki stayed in office until 2008.)

Delano Eugene Lewis was born in Arkansas City, Kan., on Nov. 12, 1939, and raised in Kansas City, Kan. His father was a porter on the Santa Fe Railroad, and his mother was a homemaker.

Mr. Lewis graduated from the University of Kansas in 1960 and received a law degree from the Washburn University School of Law in Topeka, Kan., in 1963. Mr. Lewis arrived in Washington as a young Justice Department lawyer who saw public service as a way to advance the civil rights movement. But he was soon overseas.

He was associate director for the Peace Corps in Nigeria and country director in Uganda from 1966 to 1969. After returning to Washington, he served as a legislative assistant to Sen. Edward Brooke (D-Mass.), the first Black senator popularly elected, and later worked on the staff of Del. Walter Fauntroy (D), D.C.’s representative in the House.

Mr. Lewis campaigned for the Home Rule Act, which passed in 1973 and gave the District more autonomy through a legislative council chosen by voters. Mr. Lewis made an unsuccessful run for D.C. city council in 1974, losing to Barry. (Mr. Lewis served on Barry’s mayoral transition team after his election in 1978.)

After his ambassadorship, Mr. Lewis was a senior fellow at New Mexico State University and helped create its Institute for International Relations. Mr. Lewis’s first book, “It All Begins With Self,” was published in 2015.

Survivors include his wife of 63 years, the former Gayle Jones; four sons, Delano Lewis Jr., Geoffrey Lewis, Brian Lewis and Phill Lewis, a director and actor; 11 grandchildren and four great-grandchildren.

During his time in South Africa, Mr. Lewis had made a stop at Mandela’s home for a brief meeting, he shared in a CNN interview. Mandela asked about Mr. Lewis’s family.

“The family’s fine,” Mr. Lewis recalled telling Mandela. “As a matter of fact, my wife and sister-in-law and two grandsons are in the car. And he said, ‘In the car?’ He said, ‘Bring them in.’”

Mr. Lewis’s family and Mandela gathered in the foyer of his office. Mandela reminded the two boys that their grandfather was also “an important man,” Mr. Lewis said.

“I just couldn’t handle it,” he said. “Nelson Mandela is saying that I’m an important man?”