Denby began writing film criticism while a graduate student at Stanford University's Department of Communication. He began his professional life in the early 1970s as an adherent of the film critic Pauline Kael...one of a group of film writers informally, and sometimes derisively, known as "the Paulettes." Denby wrote for The Atlantic and New York before arriving at The New Yorker in the middle 1990s; at present, Denby splits his film duties with Anthony Lane, trading off week-by-week. The schedule allows both writers to explore a broad range of critical topics in the body of the magazine.
Denby's Great Books (1996) is a non-fiction account of the Western canon-oriented Core Curriculum at his alma mater, Columbia University. Denby reenrolled after three decades, and the book operates as a kind of double portrait, as well as a sort of great-thinkers brush-up. In The New York Times, the writer Joyce Carol Oates called the book "a lively adventure of the mind," filled with "unqualified enthusiasm."Great Books was a New York Times bestseller. In The Modern Mind: An Intellectual History of the 20th Century, Peter Watson called "Great Books," the "most original response to the culture wars." The book has been published in 13 foreign editions.
In 2004, Denby published American Sucker, a memoir which details his investment misadventures in the dot-com stock market bubble, along with his own bust years as a divorcée from writer Cathleen Schine, leading to a major reassessment of his life. Allan Sloan in the New York Times called the author "formidably smart," while noting this paradox: "Mr. Denby is even smart enough to realize how paradoxical it is that he not only has a good, prestigious job, but that he is also in a position to make money by relating how he lost money in the stock market."
Snark, Denby's latest book, is a polemical dissection of public speech. He criticizes, among others, the political blog Wonkette. Wonkette responded to Denby's criticism by noting some serious factual errors in his account of the blog's work. Wonkette called out this passage in particular, a reference to a Wonkette post about Chelsea Clinton.
"But it also sounds like jealousy. Wonkette is written by young women who may have hated Chelsea’s bland words as she went around the country supporting her mother’s candidacy. When a piece of snark doesn’t make sense, some hidden fury may be screwing up the writing."
The post in question was written by one of Wonkette's two male editors (a third is female), and is clearly bylined as such. The Wonkette blog noted that Denby's incorrect assumption that the post was driven by female jealousy and fury could be seen as sexist, as well as an indication of a lack of basic research or fact-checking. Adam Sternbergh panned the book in a New York magazine review, calling snark "necessary, for reasons that Denby either ignores or fails to comprehend." Sternbergh's review led to a lengthy defense of Denby's book from writer Edward Champion.