Raised in a Roman Catholic household, he attended and graduated from Sacred Heart Cathedral Preparatory School.

[1] Diggins taught history at San Francisco State University until 1969, when he accepted a position at UC Irvine.

For a year, Diggins held the chair in American Civilization at the École des hautes études, Paris, and was also a visiting professor at Cambridge and Princeton Universities.

[2] Diggins' first book was Mussolini and Fascism: The View from America, in which he described the popularity of the Italian dictator prior to World War II and the reaction to him in the U.S.

[4] Instead of his previous left-wing assumptions about him, Diggins wrote, "Reagan was the great liberating spirit of modern American history, a political romantic impatient with the status quo.

Diggins was a consultant[citation needed] on various documentary films, including Between the Wars, Reds, John Dos Passos, The Greenwich Village Rebellion, Emma Goldman, Arguing the World,[7] The Future of the American Left, and Il Duce, Fascismo e American (Italian television).

Diggins earned a Guggenheim Fellowship in 1975, became a resident scholar at the Rockefeller Foundation in 1989, and was nominated for the National Book Award for History.

[9] After his death, the John Patrick Diggins '53 Endowed Scholarship was created in his name at Sacred Heart Preparatory School in San Francisco.

Reagan had a charitable view of human nature and a relaxed, nonjudgmental air, but there is no denying his deeply felt social conservatism.