John Leonard grew up in Washington, D.C., Jackson Heights, Queens, and Long Beach, California, where he graduated from Woodrow Wilson High School. Raised by a single mother, Ruth Smith, he made his way to Harvard University, where he immersed himself in the school newspaper, The Harvard Crimson, only to drop out in the spring of his sophomore year. He then attended the University of California at Berkeley.
Leonard was a voracious critical omnivore, writing on culture, politics, television, books and the media in many other venues, including The Nation, The New York Review of Books, Harper's, The Los Angeles Times Book Review, American Heritage and Salon.com. Leonard taught creative writing and criticism at the University of Pennsylvania and Columbia University.
Leonard wrote extensively about television in his career – for Life and The New York Times, both under the pen name Cyclops, for New York Magazine from 1984 to 2008, and in his 1997 book Smoke and Mirrors. In addition, he authored four novels and five collections of essays.
Leonard was co-literary editor of The Nation with his wife, Sue Leonard, from 1995 to 1998, and continued as a contributing editor for the magazine. He wrote a monthly column on new books for Harper's magazine and was a frequent contributor to the New York Times Book Review and The New York Review of Books. Leonard rated highest among literary critics in a 2006 Time Out New York survey of writers and publishers. He received the National Book Critics Circle’s Ivan Sandrof Lifetime Achievement Award in 2006.