The 1940 Democratic National Convention was held at the Chicago Stadium in Chicago, Illinois from July 15 to July 18, 1940. The convention resulted in the nomination of President Franklin D. Roosevelt for an unprecedented third term. Secretary of Agriculture Henry A. Wallace from Iowa was nominated for vice president.

The Twenty-second Amendment to the United States Constitution limits the number of times a person can be elected to the office of President of the United States to two terms, and sets additional eligibility conditions for presidents who succeed to the unexpired terms of their predecessors. Congress approved the Twenty-second Amendment on March 21, 1947, and submitted it to the state legislatures for ratification. That process was completed on February 27, 1951, when the requisite 36 of the 48 states had ratified the amendment, and its provisions came into force on that date.