Stevenson served in numerous positions in the federal government during the 1930s and 1940s, including the Agricultural Adjustment Administration (AAA), Federal Alcohol Administration, Department of the Navy, and the State Department. In 1945, he served on the committee that created the United Nations, and he was a member of the initial U.S. delegations to the UN. He was the 31st Governor of Illinois from 1949 to 1953, and received the Democratic Party's nomination for president in the 1952 and 1956 elections.
In both the 1952 and 1956 elections, Stevenson was defeated in landslides by Republican Dwight D. Eisenhower. He sought the Democratic presidential nomination for a third time at the 1960 Democratic National Convention, but was defeated by Senator John F. Kennedy of Massachusetts. After his election, President Kennedy appointed Stevenson as the United States Ambassador to the United Nations. He served from 1961 until his death. He died on July 14, 1965, from heart failure (after a heart attack) in London, following a United Nations conference in Switzerland. Following public memorial services in New York City, Washington, DC, and his childhood hometown of Bloomington, Illinois, he was buried in Bloomington.