Her two bestselling nonfiction books, Seabiscuit: An American Legend (2001) and Unbroken: A World War II Story of Survival, Resilience, and Redemption (2010), have sold over 13 million copies, and each was adapted for film.

Her writing style is distinct from New Journalism, dropping "verbal pyrotechnics" in favor of a stronger focus on the story itself.

"[2] Hillenbrand began her career as a freelance magazine writer, pitching and submitting stories to various publications.

Having been forced by her ill health to suspend her studies at Kenyon College in Ohio, she turned to freelance writing as a focus until she could return to school.

In fact, I still occasionally hear from people who were touched by it.”[3]Her first book was the acclaimed Seabiscuit: An American Legend (2001), a nonfiction account of the career of the great racehorse.

[4] In a C-Span record of a rare personal appearance on 29 August 2002 to promote Seabiscuit, Hillenbrand said: "When you're a journalist you get used to working for almost no money and nobody earns less than I did.

[11] Hillenbrand's essays have appeared in The New Yorker, Equus magazine, American Heritage, The Blood-Horse, Thoroughbred Times, The Backstretch, Turf and Sport Digest, and other publications.

Her 1998 American Heritage article on the horse Seabiscuit won the Eclipse Award for Magazine Writing.

Pioneers of New Journalism like Tom Wolfe and Norman Mailer wanted to blur the line between literature and reportage by infusing true stories with verbal pyrotechnics and eccentric narrative voice.

They still built stories around characters and scenes, with dialogue and interior perspective, but they cast aside the linguistic showmanship that drew attention to the writing itself.

[16][17][18] Hillenbrand spent much of her childhood riding bareback "screaming over the hills" of her father's Sharpsburg, Maryland farm.

[19] She studied at Kenyon College in Gambier, Ohio but was forced to leave before graduation when she contracted chronic fatigue syndrome, with which she has struggled ever since.

[20] Hillenbrand married Borden Flanagan, a professor of government at American University and her college sweetheart, in 2006.

[citation needed] In January 2015, she was interviewed by James Rosen of Fox News at her home in Georgetown, primarily about how she had written the book Unbroken; Rosen noted her improved health, as the interview had been put off multiple times since 2010 due to her ill health.

She mentioned in the interview how her subject, Louis Zamperini, inspired her in facing her own life problems during their many phone calls with his unfailing optimism.

She stated that her primary literary influences were writers of fiction, including Hemingway, Tolstoy, and Jane Austen.

[22] In fall 2015, Hillenbrand made a trip by road to Oregon, her first time out of Washington D. C. since 1990 that did not result in debilitating vertigo.

At Kenyon College, Hillenbrand had been an avid tennis player, cycled in the nearby country, and played football on the quad.

[10] At age 19 and in her sophomore year, Hillenbrand experienced the sudden onset of a then unknown sickness while driving back to school from spring break.

[2] By the time of her January 2015 interview with Ken Rosen, her ability to function had improved after hitting a real low during the writing of Unbroken; she increased her ability to walk down her stairs by taking one step and returning to bed, then some days later, two steps, until she could go down the whole staircase, a process that took several months.