Thomas Harry Williams (May 19, 1909 — July 8, 1979) was an American historian and author. For the majority of his academic career between the 1930s to 1970s, Williams taught history at Louisiana State University. While at LSU, Williams was a Boyd Professor of History from 1953 to 1979. Near the end of his tenure at LSU, the university created the T. Harry Williams Chair of American History. He also taught at extension schools in Wisconsin and at the Municipal University of Omaha.
As an author, Williams wrote biographical works between the 1940s to 1970s, including multiple books on Abraham Lincoln and Rutherford B. Hayes. He also wrote about P. G. T. Beauregard, the American Civil War and Huey Long. In 1970, Williams' biography of Long won the Pulitzer Prize for Biography and the National Book Award in the History and Autobiography category.
Williams received a Guggenheim Fellowship in 1956.