He was Alford Professor of Natural Religion, Moral Philosophy and Civil Polity, emeritus, at Harvard University and an authority on the work of the Greek philosopher Plato.

[2] According to the recollections of Bertrand Russell, Demos saved up and traveled steerage to the United States specifically to improve his education, having read all the books available to him at home.

[2] Arriving in Boston in 1913 without money, he first worked as a waiter in a restaurant[2] and then as a janitor in the Harvard student halls of residence in order to fund his tuition at the university.

[2] Demos was credited by Alfred North Whitehead in the preface of Science and the Modern World (1925) for reading proofs and "for the suggestion of many improvements in expression.

[8] He became Alford Professor of Natural Religion, Moral Philosophy and Civil Polity in 1945 in succession to William E. Hocking and he was a member of the Doty committee which produced the report, General Education in a Free Society, completed the same year.

[14][15] Demos died of a heart attack on 8 August 1968 while on board the S.S. Anna Maria returning to the United States.