In 2003 Berg published Kate Remembered, a biography-cum-memoir about his friendship with actress Katharine Hepburn that received mixed reviews.

"[9] After graduating from Princeton in 1971, Berg decided to expand the thesis into a full-length biography, thinking it would take around nine months.

[1][a] In 2016, The New Yorker credited Berg with "almost single-handedly rescu[ing] Maxwell Perkins from the anonymity he desired.

[20] The biography, Lindbergh, was highly anticipated; prior to its publication, the book's film rights were bought, sight unseen, by Steven Spielberg, who planned to direct a movie of it.

[21] Published in 1998, Lindbergh sold about 250,000 copies in hardcover,[22] and won the Pulitzer Prize for Biography or Autobiography.

Berg was noted for his exhaustive research,[21] as well as his sympathetic, but by no means uncritical, approach to Lindbergh, whose alleged anti-Semitism he addressed in a straightforward, unblinking manner.

[citation needed] Five years after Berg's book was published, it was revealed that Lindbergh had lived a double life, with three mistresses and secret children in Germany.

'"[24] From 1998 to 2000, Berg wrote Kate Remembered, a biography-cum-memoir detailing his 20-year friendship with the Hollywood actress Katharine Hepburn.

It spent 11 weeks on the New York Times Nonfiction Best Seller list,[26] but received uneasy critical response.

In The New York Times, Robert Gottlieb called it an "odd and unsettling book [that leaves] a sense of exploitation", and gossip columnist Liz Smith, a friend of Hepburn's, called Berg "vain and narcissistic", and declared the book "[s]elf-promoting fakery....Hepburn would have despised it and his betrayal of her friendship.

"[27][28] Berg responded in a written statement, saying that he was "truly shocked at Liz Smith's professional behaviour — or, more accurately, her lack thereof" in "her personal assault on my reputation, one that stops just short of character assassination".