Founded by Edward M. Keating as a Catholic literary quarterly, the magazine became closely associated with the New Left after executive editor Warren Hinckle hired Robert Scheer as managing editor. Its contributors included Noam Chomsky, Cesar Chavez, Seymour Hersh, Tom Hayden, Angela Davis, Jonathan Kozol, Todd Gitlin, Sol Stern, Tariq Ali, Alexander Cockburn, Christopher Hitchens and John Beecher. Unlike most leftist publications, Ramparts was expensively produced and graphically sophisticated. It reached an audience that may have been put off by the grittier "movement" publications of the time.
Between December 1966 and December 1969, newsstand sales increased from 10,000 to 42,250, and the number of subscribers jumped from 87,976 to 244,069. Between December 1969 and December 1970, the number of Ramparts' subscribers increased to 299,937. By July 1967, the magazine was also earning around $13,000 per month from its advertising sales. A share of the magazine was owned by New Republic magazine owner Martin Peretz, who became a critic of the New Left a few years later.
Ramparts was an early opponent of the Vietnam War. Its April 1966 cover article concerned the Michigan State University Group, a technical assistance program in South Vietnam that Ramparts claimed was a front for CIA covert operations. In August 1966, managing editor James F. Colaianni wrote the first national article denouncing the U.S. use of napalm in that conflict. Ramparts also unearthed the first conspiracy theory about the Kennedy assassination, and in 1967, editor Sol Stern's interview revealed that the CIA had backed the National Student Association as part of its Cold War strategy. The magazine published Che Guevara's diaries, with an introduction by Fidel Castro, and the prison diaries of Eldridge Cleaver, later republished as Soul on Ice. Cleaver was a Ramparts editor when he witnessed a confrontation between Huey Newton and a police officer outside the magazine's office in February 1967; he soon became the Black Panther Party's Minister of Information.
Although Ramparts closed its doors for good in 1975, several former staffers founded their own magazines, most notably Mother Jones and Rolling Stone. Robert Scheer later became a featured columnist in the Los Angeles Times and is now the editor of Truthdig and a regular participant in the NPR program "Left, Right and Center". Another Ramparts editor, James Ridgeway, is the Washington DC bureau chief for Mother Jones and the author of many muckraking books. James F. Colaianni went on to represent the radical Catholic perspective with the books Married Priests & Married Nuns and The Catholic Left. Two editors, David Horowitz and Peter Collier, later underwent political conversions and became neoconservative critics of the left. For a brief time, the magazine's Washington correspondent was Brit Hume, now of the Fox News Channel.
The magazine also featured discussions of arts and culture. It included contributions from (or interviews with) Thomas Merton, Allen Ginsberg, Kurt Vonnegut, Ken Kesey, Lawrence Ferlinghetti, Gabriel Garcia Marquez, Susan Sontag, Eduardo Galeano, Peter Ustinov, Erica Jong, and John Lennon.