 Hardeman served in the 52nd and 54th Legislatures representing Grayson and Collin counties in the Texas House of Representatives.Between 1958 and 1961, he worked as an assistant to Sam Rayburn, Speaker of the House, and was Rayburn's official biographer.An avid bibliophile whose book collection numbered more than ten thousand volumes, Hardeman bequeathed his collection of American biographies and political history to the LBJ Presidential Library in Austin, Texas.