Josef Berger was born on May 12, 1903 to Adolph and Sonya Berger in Denver, Colorado. He graduated from the University of Missouri School of Journalism in 1924. During the same year, while he was still attending the university, he won the McAnally Prize for Literary Composition and first place in an Atlantic Monthly essay contest. Berger proceeded to work for newspapers in Kansas City and then moved to New York, where he was a reporter and editor from 1924-1934. In 1928, Berger began writing juvenile books; his first, Captain Bib, was published in 1929. He published a total of twenty books, in addition to writing short stories and articles for publications such as Atlantic Monthly, The New Yorker, Esquire, Reader's Digest, McCall's, and The New York Times Sunday Magazine.

In 1937 Berger authored Cape Cod Pilot under the sponsorship of the Works Progress Administration's Federal Writers Project. In 1938, he received his first Guggenheim Foundation Fellowship, which he used to write In Great Waters, a history of the Portuguese in New England. He received another Guggenheim Fellowship in 1946. Berger went to Washington, D.C. in 1940 to become the editor of reports for the U.S. House of Representative Select Committee to Investigate Interstate Migration of Destitute Citizens. In 1941 he worked in the same capacity for the U.S. Senate Committee on Wartime Health and Education, followed by the position of chief speech writer for U.S. Attorney General Francis Biddle in 1942.

From 1944-1947, as chief speechwriter for the Democratic National Committee, Berger prepared speeches for Franklin Roosevelt, Harry Truman, Robert E. Hannegan, Tom Clark, Henry Wallace, Lyndon Johnson, Sam Rayburn and Estes Kefauver. The single speech he wrote for Roosevelt was scheduled to be delivered at a Jefferson Day dinner on April 13, 1945. Although Roosevelt died on April 12, the speech was subsequently published and widely quoted. Berger also served as chief of press relations for the Allied Commission on Reparations in London, Paris, Berlin, Pottsdam, and Moscow during 1945. From 1955-1968, he was the chief speechwriter for the National Foundation March of Dimes.

In an interview with Thomas Benson, a professor of Speech Communication at State University of New York in Buffalo, Benson said, "As I see it, the objective of a speech writer should be to make his principal compose as much of the speech as he can possibly get out of him. You do that by sitting across the table from him and asking him questions, as you ask me, and taking down the notes and actually making the speech his, not yours. This is good speech writing-or good ghostwriting, rather."

In 1957, Berger and his wife, Dorothy Berger, co-authored Diary of America, an anthology of diaries from colonial times to the present. Two other anthologies followed, Small Voices (1967) and First Love (1986). Poppo, a true story written in 1962, received critical acclaim and was reprinted in Reader's Digest and featured in a photo layout in Life. Berger also wrote poems and song lyrics, including a record called The Babysitters with Alan Arkin and Lee Hays.

At the age of sixty-seven, Josef Berger died suddenly of an aneurysm on November 11, 1971 in New York City.