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.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.