Thomas Underwood began his career working for the Lexington Newspaper for a brief time before being elected as a Democrat to the Eighty-first Congress and reelected to the Eighty-second Congress. He resigned on March 17, 1951, but was appointed to the United Stated Senate as a Democrat to fill a vacancy on March 19, 1951. After finishing the term, he sought reelection but lost. He returned to editorial work with the Lexington Herald.