Long before he became a grandee of public television, the Texas-born Mr. Moyers was a top aide and, by many accounts, a surrogate son to Johnson. The powerful Texas Democrat had given Mr. Moyers a summer job in his U.S. Senate office in 1954 when Mr. Moyers was in college.

Mr. Moyers arrived on Capitol Hill and, without even unpacking his bags, worked through the night addressing 275,000 envelopes using a foot-operated “addressograph” machine. By the end of the summer, he was handling Johnson’s personal correspondence.

Over the next 12 years, when he wasn’t studying or preaching — Mr. Moyers became an ordained Baptist minister in 1954 — he found his way to the highest levels of government. When Johnson was tapped in 1960 as Sen. John F. Kennedy’s (D-Massachusetts) running mate, Mr. Moyers became the liaison between the Johnson and Kennedy camps. “I could interpret Boston to Austin,” he later told journalist Don Shelby.

After Kennedy was assassinated in 1963, Mr. Moyers, not yet 30, became one of President Lyndon B. Johnson’s key lieutenants. Time magazine called him “LBJ’s young man in charge of everything.” He was named White House press secretary in July 1965.

Mr. Moyers relished his role in shaping Great Society programs to alleviate poverty and foster racial justice, but he grew rapidly disillusioned with Johnson’s escalation of the Vietnam War.

He left the White House in January 1967, in the middle of the president’s second term; Johnson, he said, never spoke to him again. According to Mimi Swartz, writing in Texas Monthly in 1989, “Johnson, who had at one time loved Moyers more than anyone else, punished him by pushing him further out of his life than anyone else.”

With a growing family to support, Mr. Moyers took a lucrative job as publisher of Newsday, the large-circulation Long Island newspaper. He tilted the paper leftward in its support of anti-war demonstrators, lured a stream of leading authors to write for its pages and led the newsroom to two Pulitzer Prizes. But his tenure was cut short in 1970 amid clashes with newspaper’s conservative owner.

Mr. Moyers then began a television career that would bring him more than 30 Emmy Awards, including one for lifetime achievement. He was mainly associated with PBS, which he joined in 1971, but he detoured to CBS from 1976 to 1986.

He enjoyed the luxuries of working for a well-funded network but resented what he perceived as the intrusion of business concerns into journalism. Conversely, at PBS, he relished his role as resident intellectual, but funding was a constant concern.

Mr. Moyers was widely known as a supporter of liberal causes — a reputation that made him a target for conservatives who viewed PBS as biased against them.

Although he frequently explored societal ills, he was happier speaking with poets and philosophers than he was with pollsters or politicians. A typical Moyers production was “Faith and Reason” (2006), a PBS series in which he asked various writers: In a world where religion is poison to some and salvation to others, how do we live together?

As editor and chief correspondent for CBS Reports beginning in 1976, he produced such documentaries as “The Fire Next Door,” about the near-destruction of the South Bronx by arson. “It’s a test,” he told viewers, “of whether democratic capitalism will be made to work for the poorest among us and the knowledge that, unless we do act, the fires will no longer stop next door.”

In 1978, he produced a show on the dangers created by the sale of baby formula in developing countries. CBS executives feared the program would scare away advertisers. When network executives forced Mr. Moyers to tone it down, People magazine reported, he sarcastically congratulated them and told them they had “turned ‘Jaws’ into ‘Gums.’”

In 1986, while filming “The Vanishing Family — Crisis in Black America,” for CBS, he asked for 90 minutes of airtime instead of the usual hour. When his bosses resisted, he threatened to quit — and got the extra time for his powerful interviews with inner-city residents about welfare, poverty and the prevalence of single-parent households. The result, documentarian Ken Burns wrote in the New York Times, was “perhaps Mr. Moyers’s single best work.”

In stature, Mr. Moyers was often described in the same breath as revered CBS newsmen Edward R. Murrow and Walter Cronkite, but he grew increasingly unhappy with the support he received from the network and he said so publicly when he left in 1986.

Two years later, PBS aired his six-part interview with Joseph Campbell, a professor who studied hero myths across cultures. Campbell’s message was that anyone — by finding a purpose and devoting his or her life to it — could take a so-called hero’s journey. The series, which treated spirituality as a route to personal fulfillment, became one of the most popular in PBS history.

Around the same time, Mr. Moyers produced a 90-minute documentary, “The Secret Government: The Constitution in Crisis,” examining the Reagan administration’s Iran-contra scandal. The show prompted some Republicans to try — unsuccessfully and in a recurring battle — to block federal funding of PBS.

After the 2002 midterm elections, Kenneth Y. Tomlinson, the chairman of the Corporation for Public Broadcasting, was incensed by Mr. Moyers’s statement on his program “Now” that the newly elected Republican Congress would “eviscerate the environment” and “force pregnant women to give up control over their own lives.”

Tomlinson complained to PBS president Pat Mitchell that the show “does not contain anything approaching the balance the law requires for public broadcasting.” PBS executives noted in response that Mr. Moyers booked many conservative commentators on “Now.”

Cultural historian Neal Gabler, writing in the Los Angeles Times in 2009, observed that Mr. Moyers was “far less interested in advancing a particular position than in inspiring moral growth in the hope of creating a more just and beneficent society.”

After leaving Newsday, Mr. Moyers embarked on a 13,000-mile road trip in which he spoke to people from all walks of life. In 1971, he published a book about those conversations, “Listening to America: A Traveler Rediscovers His Country.”

In a New York Times review, author James Dickey wrote that Mr. Moyers “relies on an unfailing faith that if people will just talk to each other, get together on issues, everything can be worked out. There is little hint of the possibility, looming more and more these days, that there are conditions that nothing can help.”

Billy Don Moyers was born in Hugo, Oklahoma, on June 5, 1934, and grew up in the northeast Texas town of Marshall. His father worked as a day laborer, while Mr. Moyers’s mother raised him and an older brother, James.

Coming from one of the poorest families in town, Mr. Moyers was frequently helped, he told Shelby, by “people older than me who saw something in me that I didn’t see.” Mr. Moyers pushed himself so hard in his academics and in his extracurriculars that, at 15, he developed ulcers.

A highlight of his youth was Johnson’s arrival by helicopter, in 1948, to make a campaign speech in Marshall.

“No microphone. No loudspeaker,” Mr. Moyers recalled to Esquire magazine. “Took his coat off. His tie was pulled back. His white shirt was glinting in the sun. And he was literally forcing himself physically on that audience of three thousand to four thousand people there on the east side of the square. I couldn’t really hear him. I was in the back row. Fourteen years old. But I remember the sheer presence of the man. And I thought, ‘That’s what power is.’”

After Mr. Moyers’s summer in Washington, Johnson persuaded him to transfer from North Texas State College in Denton (now the University of North Texas), where he was studying journalism, to the University of Texas at Austin.

In Austin he worked for KTBC radio and television, which were owned by the senator’s wife, Lady Bird Johnson. As an assistant news editor Mr. Moyers earned $100 a week — more, he said, than his father ever made and enough to allow him to marry his girlfriend, Judith Davidson, in 1954.

He was ordained that year as a Baptist minister and on Sundays he preached in the Texas Hill Country. He received a bachelor’s degree in 1956 and three years later received a master of divinity degree from the Southwestern Baptist Theological Seminary in Fort Worth.

After the Kennedy-Johnson ticket won the White House, Mr. Moyers was an assistant to the vice president but, he said, there was nothing for him or his boss to do. He began working under the president’s brother-in-law R. Sargent Shriver to create the Peace Corps. Developing its mission — to export the best of American values — he told Shelby, gave him “the happiest three years of my life.”

But Kennedy’s assassination changed everything. Back in Washington, amid the chaotic transition to a new administration, Mr. Moyers took on many tasks. He helped draft the 1964 Great Society legislation that addressed poverty, health care, education, transportation and civil rights, and played a key role in Johnson’s presidential campaign that year against conservative Sen. Barry M. Goldwater (R-Arizona).

Mr. Moyers signed off on the infamous “Daisy Ad” TV commercial, which juxtaposed footage of a girl picking flower petals with a countdown to a nuclear explosion. It is considered a progenitor of negative campaign ads that became increasingly common in later years. (“I wish I could take it back,” he told the Los Angeles Times decades later.)

As Vietnam diverted time and money from domestic programs, Mr. Moyers said, “the things I cared about were no longer priorities.” One day, he told Shelby, he looked out at the reporters in the White House briefing room and thought, “I wanted to be on their side.”

Meanwhile, Mr. Moyers had recommended his brother for a job in the press office. While working there, James Moyers developed a form of stomach cancer and killed himself in 1966. Mr. Moyers, according to Swartz, assumed financial responsibility for his brother’s wife and children.

At Newsday, which offered him four times his annual government salary of $28,000, he brought in Pete Hamill as a star columnist and published former senator Daniel Patrick Moynihan (D-New York) on the problems of the inner city and novelist Saul Bellow on the 1967 Arab-Israeli war.

The publication won major journalism awards including a Pulitzer Prize for public service for an investigation into corrupt land deals. But Harry Guggenheim, Newsday’s conservative owner, was unhappy about the paper’s direction. When Guggenheim decided to sell the paper, Mr. Moyers offered to buy it but Guggenheim declined, choosing the conservative Times-Mirror Co. instead.

In 1971, Mr. Moyers began his affiliation with WNET, a public-broadcasting station in New York. “Bill Moyers Journal,” which was syndicated to the whole PBS network over the next several years, explored such topics as the Watergate scandal and the state of America during its bicentennial. In 1986, Mr. Moyers and his wife formed an independent production company, Public Affairs Television, to create shows for PBS.

In 1996, Mr. Moyers joined the cable network MSNBC as the first host of the show “Insight.” In 2002, he returned to PBS and over the years hosted the news journal “Now With Bill Moyers” and the weekly interview show “Moyers & Company.” He wrote about a dozen books, many of them adapted from his television programs.

Mr. Moyers, who lived in Manhattan, is survived by his wife; three children, Suzanne Moyers, John D. Moyers and William Cope Moyers; six grandchildren; and a great-granddaughter. His son William Cope Moyers discussed his struggles with alcohol and crack cocaine addiction in Mr. Moyers’s 1998 documentary series “Moyers on Addiction: Close to Home.”

Of his move from presidential press secretary to journalist, Mr. Moyers told Shelby, “You learn certain things: That you’re happier if you’re trying to report the truth than if you’re trying to conceal it.”

For someone with intellectual curiosity, he added, “life is a wonderful, perpetual and eternal university.”