Hersh was born in Chicago and graducated from the University of Chicago. He began his career in journalism as a police reporter for the City News Bureau in 1959. He later became a correspondent for United Press International in South Dakota. In 1963 went on to become a Chicago and Washington DC correspondent for the Associated Press. Five years later, Hersh was hired as a reporter for The New York Times Washington Bureau, where he served from 1972 to 1975 and again in 1979.
His book The Price of Power: Kissinger in the Nixon White House won him the National Book Critics Circle Award and the Los Angeles Times book prize in biography. Hersh has written a total of eight books and contributed to the PBS television documentary, Buying the Bomb (1985).
Hersh currently contributes regularly to The New Yorker on military and security matters.