In 1944, Roosevelt appointed Hannegan, who had been the Collector of Internal Revenue in St. Louis, to the DNC after testing him by asking for his help with his income tax return. As Democratic chairman, Hannegan was responsible for brokering the deal that made Truman Roosevelt's running mate that year. Shortly before the 1944 Democratic National Convention, Roosevelt famously sent Hannegan a letter stating he would be "happy to run with" either Truman or Supreme Court Justice William O. Douglas. Vice President Henry A. Wallace nearly won the nomination, but Hannegan worked feverishly to secure Truman's nomination. Hannegan later joked he wanted his tombstone inscribed with the words "Here lies the man who stopped Henry Wallace from becoming President of the United States."