After graduating from Princeton University in 1971, Berg expanded his senior thesis on editor Maxwell Perkins into a full-length biography, Max Perkins: Editor of Genius (1978), which won a National Book Award. His second book Goldwyn: A Biography was published in 1989.
Berg's third book Lindbergh, a highly anticipated biography of aviator Charles Lindbergh was published in 1998, becoming a New York Times Best Seller, and winning the 1999 Pulitzer Prize for Biography or Autobiography. In 2003 Berg published Kate Remembered, a biography-cum-memoir about his friendship with actress Katharine Hepburn that received mixed reviews. His biography of Woodrow Wilson was published in 2013.
Berg also wrote the story for Making Love (1982), a controversial film that was the first major studio drama to address the subjects of gay love, closeted marriages, and coming out. He has contributed articles to magazines such as Architectural Digest and Vanity Fair.