[5] His mother, a Mayflower descendant, was of German and New England ancestry, as well as a relative of historian George Bancroft, according to family tradition.

[7] Schlesinger attended the Phillips Exeter Academy in New Hampshire and received his undergraduate degree at the age of 20 from Harvard College, where he graduated summa cum laude in 1938.

[9] At the time, Fellows were not allowed to pursue advanced degrees, "a requirement intended to keep them off the standard academic treadmill"; as such, Schlesinger would never earn a doctorate.

[14] In 1947, Schlesinger, together with former First Lady Eleanor Roosevelt; Minneapolis Mayor and future Senator and Vice President Hubert Humphrey; economist and longtime friend John Kenneth Galbraith; and Protestant theologian Reinhold Niebuhr[15] founded Americans for Democratic Action.

[13] After President Harry S. Truman announced he would not run for a second full term in the 1952 presidential election, Schlesinger became the primary speechwriter for and an ardent supporter of Governor Adlai E. Stevenson of Illinois.

He opposed the plan in a memorandum to the president: "at one stroke you would dissipate all the extraordinary good will which has been rising toward the new Administration through the world.

If only Castro could be induced to commit an offensive act, then the moral issue would be butted, and the anti-US campaign would be hobbled from the start.

[18]During the Cabinet deliberations, he "shrank into a chair at the far end of the table and listened in silence" as the Joint Chiefs and CIA representatives lobbied the president for an invasion.

Following the overt failure of the invasion, Schlesinger later lamented, "In the months after the Bay of Pigs, I bitterly reproached myself for having kept so silent during those crucial discussions in the cabinet room.

I can only explain my failure to do more than raise a few timid questions by reporting that one's impulse to blow the whistle on this nonsense was simply undone by the circumstances of the discussion.

"[20] After the furor died down, Kennedy joked that Schlesinger "wrote me a memorandum that will look pretty good when he gets around to writing his book on my administration.

[21] Schlesinger further warned that "by 1970 the USSR may have a radically new production technology, involving total enterprises or complexes of industries, managed by closed-loop, feedback control employing self-teaching computers".

The cause was a pre-vision of an algorithmic governance of economy by an internet-like computer network authored by Soviet scientists, particularly Alexander Kharkevich.

After his retirement from teaching in 1994, he remained an active member of the Graduate Center community as an emeritus professor until his death.

[36] He won a Pulitzer Prize for History in 1946 for his book The Age of Jackson, covering the intellectual environment of Jacksonian democracy.

His 1949 book The Vital Center made a case for the New Deal policies of Franklin D. Roosevelt and was harshly critical of both unregulated capitalism and of those liberals such as Henry A. Wallace who advocated coexistence with communism.