[10]: 127 Hersey lettered in football at Yale, where he was coached by Ducky Pond, Greasy Neale, and Gerald Ford.

After his time at Cambridge, Hersey got a summer job as private secretary and driver for author Sinclair Lewis during 1937.

He chafed at those duties, and that autumn he began work for Time,[12] for which he was hired after writing an essay on the magazine's dismal quality.

He accompanied Allied troops on their invasion of Sicily, survived four airplane crashes,[15] and was commended by the Secretary of the Navy for his role in helping evacuate wounded soldiers from Guadalcanal.

[17]: 37 After the war, during the winter of 1945–46, Hersey was in Japan, reporting for The New Yorker on the reconstruction of the devastated country, when he found a document written by a Jesuit missionary who had survived the atomic bomb dropped on Hiroshima.

[15] At exactly fifteen minutes past eight in the morning on August 6, 1945, Japanese time, at the moment when the atomic bomb flashed above Hiroshima, Miss Toshiko Sasaki, a clerk in the personnel department of the East Asia Tin Works, had just sat down at her place in the plant office and was turning her head to speak to the girl at the next desk.Soon afterward John Hersey began discussions with William Shawn, an editor for The New Yorker, about a lengthy piece on the previous summer's bombing.

He returned to America during late June and began writing the stories of six Hiroshima survivors: a German Jesuit priest, a widowed seamstress, two doctors, a minister, and a young woman who worked in a factory.

After publication of Hiroshima, Hersey noted that "the important 'flashes' and 'bulletins' are already forgotten by the time yesterday morning's paper is used to line the trash can.

[24] In 1950, during the Red Scare, Hersey was investigated by the FBI for possible Communist sympathies related to his past speeches and financial contributions, for example to the American Civil Liberties Union.

A Local Committee Sheds Light on a National Problem: Reading" (1954), about the dullness of grammar school readers in an issue of Life magazine, inspired Dr. Seuss's children's story The Cat in the Hat.

Hersey's first novel A Bell for Adano, about the Allied occupation of a Sicilian town during World War II, won the Pulitzer Prize for the Novel in 1945.

It was adapted that year as a movie of the same name, A Bell for Adano, directed by Henry King, and featuring John Hodiak and Gene Tierney.

His 1956 short novel, A Single Pebble, recounts the journey of a young American engineer traveling up the Yangtze on a river junk during the 1920s.

Hersey wrote The Algiers Motel Incident (1968), a non-fiction work about a racially motivated shooting of three young African-American men by police during the 12th Street Riot in Detroit, Michigan, in July 1967.

During 1969 he printed an elaborate broadside of an Edmund Burke quote for Elting E. Morison, a Yale history professor and fellow residential college master.

"What has kept the world safe from the bomb since 1945 has not been deterrence, in the sense of fear of specific weapons, so much as it's been memory", wrote Hersey.

[33] On October 5, 2007, the United States Postal Service announced that it would honor five journalists of the 20th century with first-class rate postage stamps, to be issued on Tuesday, April 22, 2008: Martha Gellhorn, John Hersey, George Polk, Rubén Salazar, and Eric Sevareid.

Postmaster General Jack Potter announced the stamp series at the Associated Press managing editors meeting in Washington, D.C.

Soon before Hersey's death, then Acting President of Yale Howard Lamar decided the university should honor its long-serving alumnus.

The prize is awarded to "a senior or junior for a body of journalistic work reflecting the spirit and ideals of John Hersey: engagement with moral and social issues, responsible reportage and consciousness of craftsmanship."

He was past president of the Authors League of America, and he was elected chancellor by the membership of the American Academy of Arts and Letters.