Pete Seeger, the singer, folk-song collector and songwriter who spearheaded an American folk revival and spent a long career championing folk music as both a vital heritage and a catalyst for social change, died on Monday in Manhattan. He was 94.

His death, at NewYork-Presbyterian Hospital, was confirmed by his grandson Kitama Cahill Jackson.

Mr. Seeger’s career carried him from singing at labor rallies to the Top 10, from college auditoriums to folk festivals, and from a conviction for contempt of Congress (after defying the House Un-American Activities Committee in the 1950s) to performing on the steps of the Lincoln Memorial at an inaugural concert for Barack Obama.

For Mr. Seeger, folk music and a sense of community were inseparable, and where he saw a community, he saw the possibility of political action.

In his hearty tenor, Mr. Seeger, a beanpole of a man who most often played 12-string guitar or five-string banjo, sang topical songs and children’s songs, humorous tunes and earnest anthems, always encouraging listeners to join in. His agenda paralleled the concerns of the American left: He sang for the labor movement in the 1940s and 1950s, for civil rights marches and anti-Vietnam War rallies in the 1960s, and for environmental and antiwar causes in the 1970s and beyond. “We Shall Overcome,” which Mr. Seeger adapted from old spirituals, became a civil rights anthem.

Mr. Seeger was a prime mover in the folk revival that transformed popular music in the 1950s. As a member of the Weavers, he sang hits including Lead Belly’s “Goodnight, Irene” — which reached No. 1 — and “If I Had a Hammer,” which he wrote with the group’s Lee Hays. Another of Mr. Seeger’s songs, “Where Have All the Flowers Gone?,” became an antiwar standard. And in 1965, the Byrds had a No. 1 hit with a folk-rock version of “Turn! Turn! Turn!,” Mr. Seeger’s setting of a passage from the Book of Ecclesiastes.

Mr. Seeger was a mentor to younger folk and topical singers in the ‘50s and ‘60s, among them Bob Dylan, Don McLean and Bernice Johnson Reagon, who founded Sweet Honey in the Rock. Decades later, Bruce Springsteen drew from Mr. Seeger’s repertory of traditional music about a turbulent America in recording his 2006 album, “We Shall Overcome: The Seeger Sessions,” and in 2009 he performed Woody Guthrie’s “This Land Is Your Land” with Mr. Seeger at the Obama inaugural. At a Madison Square Garden concert celebrating Mr. Seeger’s 90th birthday, Mr. Springsteen introduced him as “a living archive of America’s music and conscience, a testament of the power of song and culture to nudge history along.”

Although he recorded more than 100 albums, Mr. Seeger distrusted commercialism and was never comfortable with the idea of stardom. He invariably tried to use his celebrity to bring attention and contributions to the causes that moved him, or to the traditional songs he wanted to preserve.

Mr. Seeger saw himself as part of a continuing folk tradition, constantly recycling and revising music that had been honed by time.

During the McCarthy era Mr. Seeger’s political affiliations, including membership in the Communist Party in the 1940s, led to his being blacklisted and later indicted for contempt of Congress. The pressure broke up the Weavers, and Mr. Seeger disappeared from commercial television until the late 1960s. But he never stopped recording, performing and listening to songs from ordinary people. Through the decades, his songs have become part of America’s folklore.

“My job,” he said in 2009, “is to show folks there’s a lot of good music in this world, and if used right it may help to save the planet.”

Peter Seeger was born on May 3, 1919, to Charles Seeger, a musicologist, and Constance de Clyver Edson Seeger, a concert violinist. His parents later divorced.

He began playing the ukulele while attending Avon Old Farms, a private boarding school in Connecticut. His father and his stepmother, the composer Ruth Crawford Seeger, were collecting and transcribing rural American folk music, as were folklorists like John and Alan Lomax. He heard the five-string banjo, which would become his main instrument, when his father took him to a square-dance festival in North Carolina.

Young Pete became enthralled by rural traditions. “I liked the strident vocal tone of the singers, the vigorous dancing,” he is quoted as saying in “How Can I Keep From Singing,” a biography by David Dunaway. “The words of the songs had all the meat of life in them. Their humor had a bite, it was not trivial. Their tragedy was real, not sentimental.”

Planning to be a journalist, Mr. Seeger attended Harvard, where he founded a radical newspaper and joined the Young Communist League. After two years he dropped out and went to New York City, where Mr. Lomax introduced him to the blues singer Huddie Ledbetter, known as Lead Belly. Mr. Lomax also helped Mr. Seeger find a job cataloging and transcribing music at the Archive of American Folk Song at the Library of Congress.

Mr. Seeger met Mr. Guthrie, a songwriter who shared his love of vernacular music and agitprop ambitions, in 1940, when they performed at a benefit concert for migrant California workers. Traveling across the United States with Mr. Guthrie, Mr. Seeger picked up some of his style and repertory. He also hitchhiked and hopped freight trains by himself, trading and learning songs.

When he returned to New York later in 1940, Mr. Seeger made his first albums. He, Millard Lampell and Mr. Hays founded the Almanac Singers, who performed union songs and, until Germany invaded the Soviet Union, antiwar songs, following the Communist Party line. Mr. Guthrie soon joined the group.

During World War II the Almanac Singers’s repertory turned to patriotic, antifascist songs, bringing them a broad audience, including a prime-time national radio spot. But the singers’ earlier antiwar songs, the target of an F.B.I. investigation, came to light, and the group’s career plummeted.

Before the group completely dissolved, however, Mr. Seeger was drafted in 1942 and assigned to a unit of performers. He married Toshi-Aline Ohta while on furlough in 1943.

When he returned from the war he founded People’s Songs Inc., which published political songs and presented concerts for several years before going bankrupt. He also started his nightclub career, performing at the Village Vanguard in Greenwich Village. Mr. Seeger and Paul Robeson toured with the campaign of Henry Wallace, the Progressive Party presidential candidate, in 1948.

Mr. Seeger invested $1,700 in 17 acres of land overlooking the Hudson River in Beacon, N.Y., and began building a log cabin there in the late 1940s. (He lived in Beacon for the rest of his life.) In 1949, Mr. Seeger, Mr. Hays, Ronnie Gilbert and Fred Hellerman started working together as the Weavers. They were signed to Decca Records by Gordon Jenkins, the company’s music director and an arranger for Frank Sinatra. With Mr. Jenkins’s elaborate orchestral arrangements, the group recorded a repertoire that stretched from “If I Had a Hammer,” to a South African song, “Wimoweh” (the title was Mr. Seeger’s mishearing of “Mbube,” the name of a South African hit by Solomon Linda), to an Israeli soldiers’ song, “Tzena, Tzena, Tzena,” to a cleaned-up version of Lead Belly’s “Goodnight, Irene.” Onstage, they also sang more pointed topical songs.

In 1950 and 1951 the Weavers were national stars, with hit singles and engagements at major nightclubs. Their hits included “Kisses Sweeter Than Wine” and Mr. Guthrie’s “So Long (It’s Been Good to Know Yuh),” and they sold an estimated four million singles and albums.

Their commercial success was dampened, however, when “Red Channels,” an influential pamphlet that named performers with suspected Communist ties, appeared in June 1950 and listed Mr. Seeger, although by then he had quit the Communist Party. He later criticized himself forhaving not left the party sooner, though he continued to describe himself as a “communist with a small ‘c.’ ”

By the summer of 1951, the “Red Channels” citation and leaks from F.B.I. files had led to the cancellation of television appearances. In 1951, the Senate Internal Security Subcommittee investigated the Weavers for sedition. And in February 1952, a former member of People’s Songs testified before the House Un-American Activities Committee that three of the four Weavers were members of the Communist Party.

As engagements dried up the Weavers disbanded, though they reunited occasionally in the mid-1950s. After the group recorded an advertisement for Lucky Strike cigarettes, Mr. Seeger left, citing his objection to promoting tobacco use.

Shut out of national exposure, Mr. Seeger returned primarily to solo concerts, touring college coffeehouses, churches, schools and summer camps, building an audience for folk music among young people. He started to write a long-running column for the folk-song magazine Sing Out! And he recorded prolifically for the independent Folkways label, singing everything from children’s songs to Spanish Civil War anthems.

In 1955 he was subpoenaed by the House Un-American Activities Committee. In his testimony he said, “I feel that in my whole life I have never done anything of any conspiratorial nature.” He also stated: “I am not going to answer any questions as to my association, my philosophical or religious beliefs or my political beliefs, or how I voted in any election, or any of these private affairs. I think these are very improper questions for any American to be asked, especially under such compulsion as this.”

Mr. Seeger offered to sing the songs mentioned by the congressmen who questioned him. The committee declined.

Mr. Seeger was indicted in 1957 on 10 counts of contempt of Congress. He was convicted in 1961 and sentenced to a year in prison, but the next year an appeals court dismissed the indictment as faulty. After the indictment, Mr. Seeger’s concerts were often picketed by the John Birch Society and other rightist groups. “All those protests did was sell tickets and get me free publicity,” he later said. “The more they protested, the bigger the audiences became.”

By then the folk revival was prospering. In 1959, Mr. Seeger was among the founders of the Newport Folk Festival. The Kingston Trio’s version of Mr. Seeger’s “Where Have All the Flowers Gone?” reached the Top 40 in 1962, soon followed by Peter, Paul and Mary’s version of “If I Had a Hammer,” which rose to the Top 10.

Mr. Seeger was signed to a major label, Columbia Records, in 1961, but he remained unwelcome on network television. “Hootenanny,” an early-1960s show on ABC that capitalized on the folk revival, refused to book Mr. Seeger, causing other performers (including Bob Dylan, Joan Baez and Peter, Paul and Mary) to boycott it. “Hootenanny” eventually offered to present Mr. Seeger if he would sign a loyalty oath. He refused.

He toured the world, performing and collecting folk songs, in 1963 and returned to serenade civil rights advocates, who had made a rallying song of his “We Shall Overcome.”

Like many of Mr. Seeger’s songs, “We Shall Overcome” had convoluted traditional roots. It was based on old gospel songs, primarily “I’ll Overcome,” a hymn that striking tobacco workers had sung on a picket line in South Carolina. A slower version, “We Will Overcome,” was collected from one of the workers, Lucille Simmons, by Zilphia Horton, the musical director of the Highlander Folk School in Monteagle, Tenn., which trained union organizers.

Ms. Horton taught it to Mr. Seeger, and her version of “We Will Overcome” was published in the People’s Songs newsletter. Mr. Seeger changed “We will” to “We shall” and added verses (“We’ll walk hand in hand”). He taught it to the singers Frank Hamilton, who would join the Weavers in 1962, and Guy Carawan, who became musical director at Highlander in the ‘50s. Mr. Carawan taught the song to the Student Nonviolent Coordinating Committee at its founding convention.

The song was copyrighted by Mr. Seeger, Mr. Hamilton, Mr. Carawan and Ms. Horton. “At that time we didn’t know Lucille Simmons’s name,” Mr. Seeger wrote in his 1993 autobiography, “Where Have All the Flowers Gone.” All of the song’s royalties go to the “We Shall Overcome” Fund, administered by what is now the Highlander Research and Education Center, which provides grants to African-Americans organizing in the South.

Along with many elders of the protest-song movement, Mr. Seeger felt betrayed when Bob Dylan set aside protest songs for electric rock. When Mr. Dylan appeared at the 1965 Newport Folk Festival with a loud electric blues band, some listeners booed, and reports emerged that Mr. Seeger had tried to cut the power cable with an ax. But witnesses, including the festival’s producer, George Wein, and production manager, Joe Boyd (later a leading folk-rock record producer), said he did not go that far. (An ax was available, however. A group of prisoners had used it while singing a logging song.)

In later recountings, Mr. Seeger said he had grown angry because the music was so loud and distorted that he couldn’t hear the words.

As the United States grew divided over the Vietnam War, Mr. Seeger wrote “Waist Deep in the Big Muddy,” an antiwar song with the refrain “The big fool says to push on.” He performed the song during a taping of “The Smothers Brothers Comedy Hour” in September 1967, his return to network television, but it was cut before the show was broadcast. After the Smothers Brothers publicized the censorship, Mr. Seeger returned to perform the song for broadcast in February 1968.

During the late 1960s Mr. Seeger started an improbable project: a sailing ship that would crusade for cleaner water on the Hudson River. Between other benefit concerts he raised money to build the Clearwater, a 106-foot sloop, which was launched in June 1969 with a crew of musicians. The ship became a symbol and a rallying point for antipollution efforts and education.

In May 2009, after decades of litigation and environmental activism led by Mr. Seeger’s nonprofit environmental organization, Hudson River Sloop Clearwater, General Electric began dredging sediment containing PCBs it had dumped into the Hudson. Mr. Seeger and his wife also helped organize a yearly summer folk festival named after the Clearwater.

In the 1980s and ‘90s Mr. Seeger toured regularly with Arlo Guthrie, Woody’s son, and continued to lead singalongs and perform benefit concerts. Recognition and awards arrived. He was elected to the Songwriters Hall of Fame in 1972, and in 1993 he was given a lifetime achievement Grammy Award. In 1994 he received a Kennedy Center Honor and, from President Bill Clinton, the National Medal of Arts, America’s highest arts honor, awarded by the National Endowment for the Arts. In 1999 he traveled to Cuba to receive the Order of Félix Varela, Cuba’s highest cultural award, for his “humanistic and artistic work in defense of the environment and against racism.”

Mr. Seeger was inducted into the Rock and Roll Hall of Fame, as an early influence, in 1996. Arlo Guthrie, who paid tribute at the ceremony, mentioned that the Weavers’ hit “Goodnight, Irene” had reached No. 1, only to add, “I can’t think of a single event in Pete’s life that is probably less important to him.” Mr. Seeger made no acceptance speech, but he did lead a singalong of “Goodnight, Irene,” flanked by Stevie Wonder, David Byrne and members of the Jefferson Airplane.

Mr. Seeger won Grammy Awards for best traditional folk album in 1997, for the album “Pete” and, in 2009, for the album “At 89.” He won a Grammy in the children’s music category in 2011 for “Tomorrow’s Children.”

Mr. Seeger kept performing into the 21st century, despite a flagging voice; audiences happily sang along more loudly. He celebrated his 90th birthday, on May 3, 2009, at a Madison Square Garden concert — a benefit for Hudson River Sloop Clearwater — with Mr. Springsteen, Dave Matthews, John Mellencamp, Joan Baez, Ani DiFranco, Roger McGuinn of the Byrds, Emmylou Harris and dozens of other musicians paying tribute. That August he was back in Newport for the 50th anniversary of the Newport Folk Festival.

Mr. Seeger’s wife, Toshi, died in 2013, days before the couple’s 70th anniversary. Survivors include his son, Daniel; his daughters, Mika and Tinya; two half-sisters, Peggy, also a folk singer, and Barbara; eight grandchildren, including Mr. Jackson and the musician Tao Rodriguez-Seeger, who performed with him at the Obama inaugural; and four great-grandchildren. His half-brother Mike Seeger, a folklorist and performer who founded the New Lost City Ramblers, died in 2009.

Through the years, Mr. Seeger remained determinedly optimistic. “The key to the future of the world,” he said in 1994, “is finding the optimistic stories and letting them be known.”