James Edward Day was born on October 11, 1914, in Jacksonville, Illinois. He attended public schools in Springfield, Illinois, received his B.A. from the University of Chicago in 1935, and then attended Harvard Law School. While at Harvard, he served as the treasurer of the Lincoln's Inn Society from 1936-1937 and was the legislative editor of Harvard Law Review. He graduated from Harvard Law in 1938.

Day went to work for the firm of Sidney, Austin, Burgess and Harper in Chicago. During World War II, he trained as an officer in the Naval Reserve (1940-1942) and was called to active duty as an ensign in 1942. He was discharged as a lieutenant in 1945, returning to work for Sidney, Austin, Burgess, and Harper.

In 1948, after Adlai Stevenson was elected governor of Illinois, Day worked for Stevenson as legislative assistant and later as state insurance commissioner. He next signed on with the Prudential Insurance Company in 1953 and took charge of Prudential's western operations in 1957.

President John F. Kennedy, in order to strike a greater geographic balance within his cabinet, named Day postmaster general. In that capacity, Day is most noted for stabilizing the postal deficit through rate increases. He did not have great relations with the Kennedy administration, however, and resigned in August 1963 in order to practice law. James Edward Day died on October 29, 1996.