David Horowitz grew up a “red diaper baby” in a communist community in Sunnyside, Queens. He studied literature at Columbia, taking classes from Lionel Trilling, and became a "new leftist" during the Soviet invasion of Hungary in 1956. He did his graduate work in Chinese and English at the University of California, arriving in Berkeley in the fall of 1959. At Berkeley, he was a member of a group of radicals who in 1960 published one of the first New Left magazines, Root and Branch. In 1962 he published the first manifesto of the New Left, a book titled, Student, which described the decade’s first demonstrations.

Horowitz went to Sweden in the fall of 1962 where he began writing The Free World Colossus, his most influential leftist book. In the fall of 1963 he moved to England where he went to work for the Bertrand Russell Peace Foundation and became a protege of the Polish Marxist biographer of Trotsky, Issac Deutscher, and Ralph Miliband, an English Marxist whose sons went on to become leaders of the British Labour Party. While in England Horowitz also wrote Shakespeare: An Existential View, which was published by Tavistock Books. Under the influence of Deutscher, he also wrote Empire and Revolution: A Radical Interpretation of Contemporary History, 1969.

In 1967, Horowitz returned to the U.S. to join the staff of Ramparts Magazine, which had become a major cultural influence on the left. In 1969 he and Peter Collier, who became his lifelong friend and collaborator, took over the editorship of the magazine. Collier and Horowitz left Ramparts in 1973 to write three best selling dynastic biographies: The Rockefellers: An American Dynasty (1976); The Kennedys: An American Dream (1984); and The Fords: An American Epic (1987).

During these years Horowitz wrote two other books, The Fate of Midas, a collection of his Marxist essays and The First Frontier, a book about the creation of the United States. Following the murder of his friend Betty van Patter by the Black Panther Party in December 1972 and the victory of the Communists in Indo-China, which led to the slaughter of millions of Asians, Horowitz and Collier had second thoughts about their former comrades and commitments. In 1985 they published a cover story in the Washington Post called "Lefties for Reagan," announcing their new politics and organized a Second Thoughts Conference in Washington composed of former radicals. Four years later they published a book of the articles they had written about their new perspective and themovement they had left which they called Destructive Generation.

In 1997, Horowitz published a memoir, Radical Son(1996), about his journey from the left. George Gilder hailed it as “the first great autobiography of his generation,” and others compared the book to Whittaker Chambers' Witness.

In 1988, Horowitz and Collier created The Center for the Study of Popular Culture (the name was changed in 2006 to the David Horowitz Freedom Center) — to create a platform for his campaigns against the Left and its anti-American agendas. The DHFC is currently supported by over 100,000 individual contributors and publishes FrontpageMagazine.com, which features articles on “the war at home and abroad,” and receives approximately a million visitors per month. In 1992, Collier and Horowitz launched Heterodoxy, a print journal which confronted the phenomenon of "political correctness" focusing on the world of academia for the next ten years. In the same year he and film writer Lionel Chewynd created the "Wednesday Morning Club," the first sustained conservative presence in Hollywood in a generation. In 1996 Horowitz created the Restoration Weekend, which for the next two decades feature gatherings of leading conservative political, media and intellectual figures. In 2005 Horowitz created the website,DiscoverTheNetworks.org, an online encyclopedia of the political left, which has influenced the works of a generation of conservative journalists and authors.

With the support of the Center, Horowitz continued his writing about the nature and consequences of radical politics, writing more than a dozen books, including The Politics of Bad Faith (2000), Hating Whitey & Other Progressive Causes (2000), Left Illusions (2003), and The Party of Defeat (2008). His Art of Political War (2000) was described by Bush White House political strategist Karl Rove as “the perfect guide to winning on the political battlefield.” In 2004 he published Unholy Alliance, which was the first book about the tacit alliance between Islamo-fascists in the Middle East and secular radicals in the west.

Horowitz has devoted much of his attention over the past several years to the radicalization of the American university. In 2001 he conducted a national campaign on American campuses to oppose reparations for slavery 137 years after the fact as divisive and racist, since the since there were no longer any living slaves and reparations were to be paid and received on the basis of skin color). His book Uncivil Wars (2001) describes the campaign and was the first in a series of five books he would write about the state of higher education.

In 2003, he launched an academic freedom campaign to return the American university to traditional principles of open inquiry and to halt indoctrination in the classroom. To further these goals he devised an Academic Bill of Rights to ensure students access to more than one side of controversial issues and to protect their academic freedom. In 2006, Horowitz published The Professors (2006), a study of the political abuse of college classrooms. Indoctrination U., which followed in 2008, documented the controversies this book and his campaign had created. In 2009, he co-authored One Party Classroom with Jacob Laksin, a study of more than 150 college curricula designed as courses of indoctrination. In 2010, he published Reforming Our Universities, providing a detailed account of the entire campaign.

Along with these titles Horowitz wrote two philosophical meditations/memoirs on mortality, The End of Time (2005) and A Point in Time (2011), which summed up the themes of his life. A Cracking of the Heart (2009) is a poignant memoir of his daughter Sarah which explores these themes as well.

Many have commented on the lyrical style of these memoirs. The literary critic Stanley Fish, a political liberal, has described The End of Time as “Beautifully written, unflinching in its contemplation of the abyss, and yet finally hopeful in its acceptance of human finitude.”

In 2013 Horowitz began publishing a ten volume series of his collected journalistic writings and essays under the general title The Black Book of The American Left. The first volume, My Life & Times, was published in 2013; the second, Progressives, in 2014. The Black Book is filled with character and event—with profiles of radicals he knew (ranging from Huey Newton to Billy Ayers), analysis of the nature of progressivism, and running accounts of his efforts to oppose it. When completed, The Black Book will be a unique chronicle of the political wars between left and right as seen by an observer who has made a significant impact on both sides of the during his political and literary careers.

Cultural critic Camille Paglia has said of David Horowitz: “I respect the astute and rigorously unsentimental David Horowitz as one of America’s most original and courageous political analysts. . . . I think that, a century from now, cultural historians will find David Horowitz’s spiritual and political odyssey paradigmatic for our time.”

Norman Podhoretz, former editor of Commentary magazine, says of Horowitz: “David Horowitz is hated by the Left because he is not only an apostate but has been even more relentless and aggressive in attacking his former political allies than some of us who preceded him in what I once called ‘breaking ranks’ with that world. He has also taken the polemical and organizational techniques he learned in his days on the left, and figured out how to use them against the Left, whose vulnerabilities he knows in his bones.”

A full bibliography of Horowitz’s writings is available at: http://www.frontpagemag.com/bibliography