Seeger's career was marked by controversy. From the start, he aspired to use folk music to promote his left-wing political views, and in times of national turmoil that brought him into direct confrontation with the U.S. government, corporate interests, and people who did not share his beliefs. These conflicts shaped his career. At times, his exposure through the mass media was extremely limited, and he was even threatened with imprisonment. That he accepted such challenges was a measure of his commitment to his ideals, which completely superseded any interest in being a conventional entertainer. Indeed, he scorned the trappings of mainstream popular success; his goals were to inspire and instruct, not merely to entertain. So, it might be most accurate to say of Pete Seeger that he devoted his life to such causes as building unions, ending wars, supporting the rights of the oppressed, and saving the environment, and that his means of expressing that devotion took the form of singing and playing on the banjo and the guitar old songs that had been revised to address those causes.

He was born Peter R. Seeger in New York City on May 3, 1919, to the musicologist Charles Louis Seeger, Jr., and the violinist Constance de Clyver (Edson) Seeger. Naturally, he was encouraged to learn music by his parents, who gave him a violin and a ukulele when he was eight. He preferred the ukulele, and he eschewed formal music lessons. In the summer of 1936, his father took him to the Ninth Annual Folk Song and Dance Festival in Asheville, NC, where he discovered the five-string banjo. That fall, he began attending Harvard. He dropped out before the end of his sophomore year and moved to New York to try to become a journalist, but only found employment singing and playing the banjo. In 1939, he moved to Washington, D.C., to work at the Archive of American Folk Song at the Library of Congress.

On March 3, 1940, Seeger was among the performers at a benefit for California migratory workers held in New York. There he met Woody Guthrie. By May, Seeger and Guthrie had hit the road for a visit to Guthrie's home in Oklahoma. They performed together along the way. Back in New York late in the year, he met Lee Hays and Millard Lampell, and they formed the politically oriented group the Almanac Singers. They recorded a series of albums, but disbanded in 1942 as their members entered military service in World War II. Seeger was inducted into the army in July 1942 and served until December 1945, then returned to performing, now as a solo artist. In late 1948, he and Hays discussed putting together a new folk group. They were joined by Ronnie Gilbert and Fred Hellerman in a quartet named the Weavers. In January 1949, Seeger (music) and Hays (lyrics) wrote "The Hammer Song" (aka "If I Had a Hammer"), a stirring anthem that the Weavers began to perform at political events and eventually recorded for the tiny Charter Records label. Having achieved little recognition in a year of existence, the Weavers considered disbanding at the end of 1949, but instead, Seeger got them a booking at the Village Vanguard, and as they continued to appear there over a period of months, they finally began to get notice. Meanwhile, Seeger had sold some recordings he had made in Los Angeles in 1947 to Folkways Records, resulting in the release in 1950 of his first formal solo album, Darling Corey. But he gained much greater exposure from his work with the Weavers, who were signed to Decca Records and began recording in May. Their first Decca single combined an Israeli folk song, "Tzena Tzena Tzena," with Leadbelly's "Goodnight Irene." "Tzena Tzena Tzena" peaked at number two, and "Goodnight Irene" hit number one for the first of 13 consecutive weeks on August 19, 1950. The Weavers followed with seven more chart hits through the spring of 1952, among them Guthrie's "So Long (It's Been Good to Know Yuh)," "On Top of Old Smoky," "Kisses Sweeter than Wine," and "Wimoweh." Due to their left-wing leanings, however, they were caught up in the anti-Communist witch hunts of the early '50s and forced to disband by early 1953. They managed to re-form in late 1955, and Seeger performed and recorded with them through 1958. Meanwhile, he had had his own problems with red-baiting. He was called to testify by the Committee on Un-American Activities of the House of Representatives on August 18, 1955. After refusing to answer the committee's questions, he was cited for ten counts of contempt of Congress in 1956 and indicted in 1957.

After the breakup of the Weavers in 1953, Seeger went back to solo work, performing in any venue that would have him, including schools and summer camps. He began recording extensively for Folkways, turning out children's records; albums of traditional folk songs; albums of original songs; albums of topical songs; instructional records on how to play musical instruments; and live recordings. By the end of 1960, a full-scale folk music revival was underway, fostered by Seeger and the Weavers, who had inspired such popular acts as the Kingston Trio. John Hammond, a record executive at Columbia Records, was determined to build Columbia's standing in the folk market. He took the bold step of signing Seeger to his first major-label recording contract since the Weavers had been on Decca. It was a highly unusual action. Not only was Seeger still under indictment, with a trial coming up shortly, but Columbia also had to contend with Folkways, which had a backlog of Seeger recordings. Columbia agreed not only that Folkways could release Seeger tracks from its vault, but that if he recorded material Columbia did not care to release, he was "free to take it to a smaller label." It was a loophole big enough to drive a truck through, and, in effect, Seeger was never an "exclusive" Columbia recording artist; he went right on recording for Folkways.

On April 4, 1961, Seeger was found guilty of contempt of Congress and sentenced to ten concurrent one-year terms in prison. He immediately appealed, and he was acquitted on May 18, 1962. On April 30, 1961, he performed at the Village Gate, where Hammond recorded his debut Columbia album as a live disc entitled Story Songs. It was released August 14 1961. Seeger's second Columbia album, The Bitter and the Sweet (November 12, 1962), was also a live album. Included on it was the philosophical "Turn! Turn! Turn! (To Everything There Is a Season)." Three years later, the song was released in a folk-rock arrangement by the Byrds and became a number-one hit. Seeger's third Columbia LP, Children's Concert at Town Hall (April 21, 1963) was another live disc. In early 1962, he scored an unexpected hit as a songwriter when the Kingston Trio's cover of "Where Have All the Flowers Gone" became a Top 40 hit. (Johnny Rivers also scored a Top 40 hit when he revived it in 1965.) Also, in the summer of 1962, Peter, Paul & Mary released as a single their re-harmonized version of the 1949 Seeger/Hays anthem "If I Had a Hammer (The Hammer Song)." It became a Top Ten hit. A year later, Latin pop singer Trini Lopez revived it, and his version made the Top Five.

Seeger made a historic appearance at Carnegie Hall in June 1963. His concert produced his fourth consecutive Columbia live album, We Shall Overcome. In addition to the title song, which he contributed to and helped popularize, he also sang "Guantanamera," his adaptation of a poem by the Cuban poet José Marti. Three years later, the song was recorded by the Sandpipers and became a Top Ten hit. And the show featured Seeger's performance of the satiric song "Little Boxes," written by Malvina Reynolds. Released as a single, it became Seeger's only chart entry as a performer in early 1964.

Seeger and his family left the U.S. for a round-the-world trip on August 18, 1963. Gone for ten months, they traveled through 24 countries. In his absence, the folk music revival arguably peaked and went into decline. The We Shall Overcome LP was released on October 14, 1963, and became his first chart hit as a solo artist, reaching the Top 50 in Billboard. Milking the success of We Shall Overcome, Columbia held off on releasing another Seeger album for 13 months; his fifth live album for the label, I Can See a New Day, finally appeared on November 16, 1964. Folkways, meanwhile, in addition to releasing its own Seeger albums, also licensed material to other labels, resulting in the appearance of Folk Songs by Pete Seeger on Capitol Records in 1964 and several LPs, starting with Pete Seeger on Campus, on the joint venture Verve/Folkways Records in 1965-1966. Columbia raised no objections to these actions, perhaps because it was losing interest in the singer. After the release of yet another live album, Strangers and Cousins in June 1965, the label allowed its contract with Seeger to lapse, only to re-sign him shortly afterward at Hammond's insistence.

With the Vietnam War heating up, the civil rights struggle becoming more radical, and folk music giving way to folk-rock, Seeger seems to have become increasingly frustrated in 1965. As his first Columbia studio LP, God Bless the Grass, released on January 17, 1966, would show, he was becoming more interested in the nascent environmental movement, particularly in cleaning up the polluted Hudson River that ran by his home. Soon, he would conceive the idea of building a sloop like the ones that had plied the river at the turn of the century as a means of promoting ecology. His next Columbia album, Dangerous Songs!?, recorded in February 1966 and released later in the year, contained traditional topical songs. In the fall, he began recording Waist Deep in the Big Muddy and Other Love Songs, featuring some folk-rock arrangements. It became known for the political allegory of its title song, which told the story of an army unit on patrol near the Mississippi River in the '40s being led into a quagmire by a misguided commanding officer: "The big fool says to push on," Seeger sang. Of course, the song was really about President Lyndon Johnson and the Vietnam War. Columbia released the LP on July 17, 1967. On September 10, the folk-comedy duo the Smothers Brothers broke the blacklist that had kept Seeger off of network television for 17 years by having him as a guest on their CBS variety show The Smothers Brothers Comedy Hour. It had been intended that he sing "Waist Deep in the Big Muddy," but the network censors deleted the song from his appearance. When this was revealed, it gave the song even greater exposure. The network finally relented, and Seeger returned to the show to sing the song in February 1968.

Seeger recorded and released a new live album for Columbia, Pete Seeger Now, in 1968. On it, he continued to criticize the Vietnam War. By 1969, he was focusing on the building of the Hudson River sloop, to be called the Clearwater. He did some recording for Columbia in March to fill up an album of stray tracks called Young vs. Old, released August 6. Having been built in Maine, the Clearwater was launched on June 27, 1969, and Seeger and his crew sailed it down the New England coast and into the Hudson River, giving concerts along the way. In 1970, Seeger accepted an invitation from director Otto Preminger to write and perform a song in the feature film Tell Me That You Love Me, Junie Moon. The song was "Old Devil Time," which Seeger also used on his next and last Columbia album, Rainbow Race, released on June 23, 1971.

Seeger was less active for a period in 1972-1974 because of medical problems. He returned to action in 1974, appearing with the Reverend Frederick Douglass Kirkpatrick on the children's television series Sesame Street, which led to the release of a children's LP, Pete Seeger and Brother Kirk Visit Sesame Street. In December, Folkways released his first new solo studio album in three-and-a-half years, Banks of Marble and Other Songs. He went out on the first of a series of tours with Arlo Guthrie, leading to the release of a double-LP live album, Together Again, on Warner Bros. Records in 1975, and it spent a few weeks in the charts. Signed to Warner Bros. as a solo artist, Seeger recorded a final major-label studio album, Circles and Seasons, and it was released in 1979. On January 11, 1980, he persuaded Folkways to record a full-length show he performed at Sanders Theatre on the campus of Harvard in Cambridge, MA, as what he called a "demonstration concert" to show his techniques in song-leading. The album, Singalong, was released initially as a two-LP boxed set.

Seeger recorded infrequently in the '80s and ‘90s. But he accepted an offer from his friend Paul Winter to make an album for Winter's Living Music label, resulting in the release of Pete on April 16, 1996. It won him his first Grammy Award for Best Traditional Folk Album. Appleseed Records assembled the Seeger tribute albums Where Have All the Flowers Gone: The Songs of Pete Seeger (March 17, 1998) and If I Had a Song: The Songs of Pete Seeger, Vol. 2 (October 9, 2001), both various-artists collections. The label's third tribute album, Seeds: The Songs of Pete Seeger, Vol. 3 (September 23, 2003), was credited to Pete Seeger and Friends and featured an entire disc of Seeger's own recordings. In 2008, he made one more solo album for Appleseed, Pete Seeger at 89. Released on September 30, it won the 2008 Grammy Award for Best Traditional Folk Album. Seeger's 90th birthday on May 3, 2009, was celebrated with an all-star concert at Madison Square Garden at which he performed with many of the artists he had influenced over the years.