The trio Peter, Paul, and Mary became one of the most well-known folk performers of the 1960s because to Peter Yarrow’s compassionate and morally upright singing. He passed away on Tuesday at his Upper West Side Manhattan home. He was eighty-six.

His publicist, Ken Sunshine, announced his demise. Bladder cancer, which Mr. Yarrow had been fighting for the previous four years, was the reason, according to Mr. Sunshine.

The three divides the vocal parts equally on many of their albums, encircling Mary Travers’s warm contralto and Noel Paul Stookey’s soft baritone with Mr. Yarrow’s precise tenor. However, Mr. Yarrow also had some notable lead vocals, fronting well-known group songs that he either composed or co-authored, including “Day Is Done,” “Puff the Magic Dragon,” and “The Great Mandala.” “Day Is Done” made it into the Top 20, and “Puff” rose to the No. 2 spot on the Billboard charts.

Many more songs that were recorded by the group were written by Mr. Yarrow, frequently in cooperation with Mr. Stookey, the group’s final living member (Ms. Travers passed away in 2009 at the age of 72).

During their best years, Peter, Paul, and Mary made 12 appearances in the Billboard Top 40; six of those tracks, including their No. 1 cover of John Denver’s “Leavin’ on a Jet Plane,” made it into the Top 10. They had two albums at the top of the magazine’s album chart and five albums in the Billboard Top 10.

Peter, Paul, and Mary were as well-known for their progressive politics as their music, as were many other folk groups of the era. They participated in the March on Washington in August 1963, where the Rev. Dr. Martin Luther King Jr.speech titled “I Have a Dream.” They sang Bob Dylan’s “Blowin’ in the Wind,” which they had made a Top Five Billboard hit that month, on the steps of the Lincoln Memorial. Their performance in Washington contributed to the song’s status as a civil rights anthem.

In addition, the trio performed live and recorded songs in support of liberal presidential candidates George McGovern in 1972 and Eugene McCarthy in 1968. The group’s political dedication was frequently highlighted in Mr. Yarrow’s lyrics: “The Great Mandala,” which was released in 1967, detailed the story of a war protester who went on a hunger strike; “Day Is Done,” which was written in 1969 and addressed to his son, implies that the next generation may bring about a more equitable world.

Children’s songs “Day Is Done” and “Puff the Magic Dragon” both had straightforward sing-along choruses and resolutely naïve points of view. Mr. Yarrow transformed each of them into an illustrated children’s book decades later. In 1978, “Puff” also sparked an animated television special that became so successful that it led to two follow-ups.

Bernard and Vera (Burtakoff) Yarrow, Jewish immigrants from Ukraine, welcomed Peter Yarrow into the world on May 31, 1938, in Manhattan. His father practiced law and worked for Thomas E. Dewey as an associate district attorney in New York. Later on, he rose to the position of vice president at Radio Free Europe, an outfit supported by the C.I.A.

When Mr. Yarrow was five years old, his parents were divorced. Later, his father became a Protestant, but Mr. Yarrow thought that Jewish ideas were very important.

When Mr. Yarrow was five years old, his parents were divorced. Mr. Yarrow saw Jewish ideas as a significant source of inspiration in his life, even if his father subsequently became a Protestant.

At the High School of Music and Art in Manhattan, which is now the Fiorello H. LaGuardia High School of Music & Art and Performing Arts, he pursued painting studies. He took a course in American folk literature given by the folklorist and historian Harold William Thompson during his college years at Cornell, when he also started playing guitar and singing.

Mr. Yarrow relocated to New York City after graduating and started performing in the thriving Greenwich Village folk scene. In 2015, he told the music journal Rebeat, “I went with the idea that I want to be involved in music that creates community”—music that “reaches people’s hearts and mobilizes people for a more humane society.”

His popularity in the Village earned him a spot on the 1960 CBS television program “Folk Sound USA.” Additionally, it gave him the opportunity to perform at the Newport Folk Festival, where he got to know Albert Grossman, the festival’s founder and Odetta’s manager.

The Weavers were a folk harmony group with three men (including Pete Seeger) and a woman that achieved great popularity in the 1950s. Mr. Grossman intended to build a new group that would update and improve on their formula. He matched Mr. Yarrow with Ms. Travers, who had performed with Mr. Seeger on multiple occasions and in Village clubs. At Ms. Travers’s suggestion, they added Noel Paul Stookey, with whom she had performed at a local club, transforming the duo into a three. The catchy biblical moniker they chose was Mr. Stookey’s middle name.

The trio made a striking visual impression: Ms. Travers, whose blond hair highlighted aristocratic cheekbones, was surrounded by two guys with dark ties, beatnik goatees, and solemn looks. Buzz was created when Mr. Grossman arranged for them to run at Bleecker Street’s Bitter End. The quartet signed with Warner Bros. Records in 1961, and the following May, they released their debut album, simply titled “Peter, Paul, and Mary.”

The group’s first record, “Lemon Tree,” which was based on a Brazilian folk song and peaked at number 40 on the Billboard charts, featured lead vocals by Mr. Yarrow. After the Weavers’ second single, “If I Had a Hammer,” which was penned by Pete Seeger and Lee Hays, went on to become a Top 10 hit and win two Grammy Awards, the entire album shot to the top of the charts. The record sold over two million copies and spent two years in the Top 20.

The song “Puff the Magic Dragon” from the group’s follow-up, “Movin’,” which was published in early 1963, was based on a poem that Mr. Yarrow’s friend Lenny Lipton had written when he was 19 years old. The poem was influenced by an older poem by Ogden Nash called “The Tale of Custard the Dragon.” Later, there was conjecture that the song was about smoking marijuana, which Mr. Yarrow vehemently refuted.

The trio’s rendition of “Blowin’ in the Wind” was released in June 1963. (Mr. Grossman also had Bob Dylan as a client.) In its first week, an estimated 300,000 copies were sold. It peaked at number two by the middle of August and sold over a million copies.

The writer’s own album, “The Freewheelin’ Bob Dylan,” shot into the Top 30 after their rendition of another Dylan song, “Don’t Think Twice, It’s All Right,” broke the Billboard Top 10.

Mr. Yarrow became a member of the Newport Folk Festival board in 1964. He came up with the idea for the New Folks Concert during the Kerrville Folk Festival in Texas in 1970, and it has since grown into a yearly occasion. He had assisted in planning the National Mobilization to End the War, a demonstration against the Vietnam War that drew an estimated half a million people to Washington the previous year.

In 1970, “Leavin’ on a Jet Plane,” which featured Ms. Travers’s longing contralto, became the biggest hit of Peter, Paul, and Mary’s career. However, they announced their separation a few months later.

In 1969, Mr. Yarrow was accused of making sexual attempts on a 14-year-old girl who had come to his dressing room with her 17-year-old sister to get an autograph. This was one of the reasons they split up, although they also did so to pursue solo careers. He admitted to taking “indecent liberties” with the girl and was sentenced to three months of a one-to-three-year prison term.

Jimmy Carter granted Mr. Yarrow a presidential pardon in 1981, but the case persisted for many years during the electoral campaigns of the politicians Mr. Yarrow backed.

Mr. Yarrow’s scheduled performance at an upstate New York arts festival was canceled in reaction to protests in 2019, during the height of the #MeToo campaign against sexual mistreatment of women. In a statement, an apologetic Mr. Yarrow retorted that the decision by the organizers to exclude him was neither “unfair or unjust.”

In a statement to The New York Times, he stated, “I cannot adequately express my apologies and sorrow for the pain and injury I have caused, and I do not seek to minimize or excuse what I have done.”

Marybeth McCarthy, a niece of Democratic presidential candidate Eugene McCarthy, was married to Mr. Yarrow in 1969. (Mr. Stookey created “Wedding Song,” which has since been sung at wedding ceremonies all across the world in their honor.) After a divorce, they got married again in 2022. Along with her, Mr. Yarrow has a daughter, Bethany; a granddaughter; and a son, Christopher.

“Peter,” Mr. Yarrow’s debut solo album, was released in 1972, although sales were not very strong. Four years later, he had even more success with “Torn Between Two Lovers,” a song he co-wrote with Phillip Jarrell that became a No. 1 hit for Mary MacGregor, a mediocre pop singer.

In 1972 and 1978, Peter, Paul, and Mary got back together for special benefit concerts. They started touring often after their second reunion, and they kept performing until Ms. Travers passed away. Since then, Mr. Stookey and Mr. Yarrow have occasionally performed together.

He also “grew to be grateful for, and to love, the mature-beyond-his-years wisdom and inspiring guidance he shared with me like an older brother,” Mr. Stookey said in a statement on Tuesday, referring to Mr. Yarrow as his “creative, irrepressible, spontaneous and musical younger brother.”

Mr. Stookey remarked, “I will miss Peter and his brother very much. Perhaps he was both of the brothers I never had.”

In 1972 and 1978, Peter, Paul, and Mary got back together for special benefit concerts. They started touring often after their second reunion, and they kept performing until Ms. Travers passed away. Since then, Mr. Stookey and Mr. Yarrow have occasionally performed together.

He also “grew to be grateful for, and to love, the mature-beyond-his-years wisdom and inspiring guidance he shared with me like an older brother,” Mr. Stookey said in a statement on Tuesday, referring to Mr. Yarrow as his “creative, irrepressible, spontaneous and musical younger brother.”

Mr. Stookey remarked, “I will miss Peter and his brother very much. Perhaps he was both of the brothers I never had.”

Mr. Yarrow assisted in the founding of Operation Respect in 2000, a nonprofit organization aimed at preventing bullying and encouraging tolerance among kids.

In his later years, he frequently played as part of the trio Peter, Bethany, and Rufus, which included his daughter and cellist Rufus Cappadocia. Mr. Yarrow’s confidence in his genre was strengthened by their success.

In 2008, he told Reuters, “I think folk music has had a positive effect on the decency, humanity, and empathy of society.” Some of the large crowd that Peter, Paul, and Mary addressed disagreed with our political stance. However, the human quality of our music moved them.