During World War I, Ely worked to build popular support for the American war effort, taking part in the activities of the League to Enforce Peace. He headed the committee of arrangements for a "Win the War Convention" held in Madison from November 8–10, 1918. Ely's political activities during World War I included his campaign against Senator Robert M. La Follette. Although La Follette was a Progressive in politics, he did not support the war, and so Ely regarded him as unfit for office. Ely tried to have him removed from the United States Senate and end his influence in Wisconsin politics.