He was 94.
Seeger, who lived in the Hudson Valley city of Beacon, N.Y., died of natural causes at NewYork-Presbyterian Hospital Monday, Kitama Cahill Jackson told the New York Times.
Seeger became a fixture on nationwide radio in the 1940s and had a string of hit records in the early 1950s as a member of the Weavers folk music quartet.
The group's most famous recording was of Lead Belly's "Goodnight, Irene," which topped the charts for 13 weeks in 1950.
Members of the Weavers were blacklisted during the McCarthy Era.
In the 1960s, Seeger re-emerged as a prominent singer of protest music in support of international disarmament, civil rights and environmental causes.
He was one of the folksingers who popularized the spiritual "We Shall Overcome" during the 1960s U.S. civil rights movement.
Seeger's "Turn! Turn! Turn!" -- a folk rock setting of a passage from the Book of Ecclesiastes -- became a No. 1 hit for the Los Angeles rock band the Byrds in 1965.
During his long career, Seeger sang at labor rallies, headlined folk music festivals and performed on the steps of the Lincoln Memorial at a concert for President Barack Obama's first inauguration.
He told United Press International in 1985 he saw his career as a link to a long history of songs written and sung by working people.
"My job is to pass on the songs and music I've learned," he said. "I'm a link to a long line of people like Woody Guthrie and Lead Belly. They taught songs to me and I've taught them to others."
At a Madison Square Garden concert celebrating Seeger's 90th birthday, Bruce 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."
Seeger's wife, Toshi, died last year, days before the couple's 70th anniversary.
He is survived by a son, Daniel; daughters, Mika and Tinya; a half-sister, Peggy; and six grandchildren, including musician Tao Rodriguez-Seeger, who performed with him at Obama's inauguration.
The president issued a statement Tuesday, celebrating Seeger's life and work.
"Once called 'America's tuning fork,' Pete Seeger believed deeply in the power of song," Obama said in the statement. "But more importantly, he believed in the power of community -- to stand up for what's right, speak out against what's wrong, and move this country closer to the America he knew we could be. Over the years, Pete used his voice -- and his hammer -- to strike blows for worker's rights and civil rights; world peace and environmental conservation. And he always invited us to sing along. For reminding us where we come from and showing us where we need to go, we will always be grateful to Pete Seeger. Michelle and I send our thoughts and prayers to Pete's family and all those who loved him."