Mcmillan was elected as a Democrat to the Seventy-sixth Congress by special election, on November 7, 1939, to fill the vacancy caused by the death of her husband, Thomas S. McMillan, and served from November 7, 1939, to January 3, 1941.[1] She was not a candidate for reelection in 1940 to the Seventy-seventh Congress. She served in National Youth Administration, then the Office of Government Reports, Office of War Information, 1941. She was appointed information liaison officer for the Department of State, Washington, D.C., on January 1, 1946, and served until July 31, 1957.