Longest Serving U.S. Senators Fast Facts (CNN) -- Here's a look at the top 20 longest-serving senators in United States history. The Top Twenty as of 8/28/2013: Names in bold are currently serving in the U.S. Senate 1) Robert C. Byrd (D-WV), 51 years, 5 months, 26 days January 3, 1959 to June 28, 2010 2) Daniel K. Inouye (D-HI), 49 years, 11 months, 14 days January 3, 1963 to December 17, 2012 3) Strom Thurmond (R-SC), 47 years, 5 months, 8 days December 14, 1954 to April 4, 1956 November 7, 1956 to January 3, 2003 4) Edward M. Kennedy (D-MA), 46 years, 9 months, 19 days November 7, 1962 until his death on August 25, 2009 5) Carl T. Hayden (D-AZ), 41 years, 9 months, 30 days March 4, 1927 to January 2, 1969 6) John C. Stennis (D-MS), 41 years, 1 month, 29 days November 5, 1947 to January 2, 1989 7) Theodore F. Stevens (R-AK), 40 years, 10 days December 24, 1968 to January 3, 2009 8) Patrick Leahy (D-VT), 38 years, 7 months, 26 days as of 8/28/2013 January 3, 1975 - present 9) Ernest F. Hollings (D-SC), 38 years, 1 month, 25 days November 9, 1966 to January 3, 2005 10) Richard B. Russell (D-GA), 38 years, 10 days January 12, 1933 to January 21, 1971 11) Russell Long (D-LA), 38 years, 3 days December 31, 1948 to January 2, 1987 12) Francis E. Warren (R-WY), 37 years, 4 days November 18, 1890 to March 3, 1893 March 4, 1895 to November 24, 1929 13) Orrin Hatch (R-UT), 36 years, 7 months, 26 days as of 8/28/2013 January 3, 1977 to present 14) James O. Eastland (D-MS), 36 years, 2 months, 24 days June 30, 1941 to September 28, 1941 January 3, 1943 to December 27, 1978 15) Warren Magnuson (D-WA), 36 years, 20 days December 14, 1944 to January 2, 1981 16) Joseph R. Biden, Jr. (D-DE), 36 years, 13 days January 3, 1973 to January 20, 2009 17) Pete V. Domenici (R-NM), 36 years January 3, 1973 to January 3, 2009 17) Richard Lugar (R-IN), 36 years January 3, 1977 to January 3, 2013 17) Claiborne Pell (D-RI), 36 years January 3, 1961 to January 3, 1997 20) Kenneth McKellar (D-TN), 35 years, 10 months March 4, 1917 to January 2, 1953