Montana was admitted to the Union on November 8, 1889, and elects U.S. senators to classes 1 and 2. Its current U.S. senators are Democrat Jon Tester (serving since 2007) and Republican Steve Daines (serving since 2015), making it one of five states to have a United States Senate delegation split between Republican and Democratic caucusing senators. Max Baucus is the state's longest serving senator, serving from 1978 to 2014.
|- style="height:2em"| colspan=3 | Vacant| nowrap | Nov 8, 1889 –
Jan 1, 1890| Montana elected its first senators two months after admission to the Union.| rowspan=3 | 1| rowspan=2 | rowspan=5 | 1| Montana elected its first senators two months after admission to the Union.| nowrap | Nov 8, 1889 –
Jan 2, 1890| colspan=3 | Vacant
|- style="height:2em"! rowspan=2 | 1| rowspan=2 align=left |
Wilbur F. Sanders| rowspan=2 | Republican| rowspan=2 nowrap | Jan 1, 1890 –
Mar 3, 1893| rowspan=2 | Elected in 1890.Lost re-election.| rowspan=4 | Elected in 1890.Retired.| rowspan=4 nowrap | Jan 2, 1890 –
Mar 3, 1895| rowspan=4 | Republican| rowspan=4 align=right |
Thomas C. Power! rowspan=4 | 1
|- style="height:2em"|
|- style="height:2em"| colspan=3 | Vacant| nowrap | Mar 3, 1893 –
Jan 16, 1895| Legislature failed to elect.| rowspan=4 | 2| rowspan=2
|- style="height:2em"! rowspan=3 | 2| rowspan=3 align=left |
Lee Mantle| rowspan=2 | Republican| rowspan=3 nowrap | Jan 16, 1895 –
Mar 3, 1899| rowspan=3 | Elected to finish vacant term.Lost renomination.
|- style="height:2em"| | rowspan=4 | 2| rowspan=4 | Elected in Jan 1895.[1] Lost re-election.| rowspan=4 nowrap | Mar 4, 1895 –
Mar 3, 1901| rowspan=4 | Republican| rowspan=4 align=right |
Thomas H. Carter! rowspan=4 | 2
|- style="height:2em"| | Silver
Republican|
|- style="height:2em"! 3| align=left |
William Clark| | Democratic| nowrap | Mar 4, 1899 –
May 15, 1900| Elected in 1899.Resigned to avoid claim of election fraud.| rowspan=5 | 3| rowspan=2
|- style="height:2em"| rowspan=2 colspan=3 | Vacant| rowspan=2 nowrap | May 15, 1900 –
Mar 7, 1901| rowspan=2 | Clark was appointed to continue his term, but did not qualify.
|- style="height:2em"| rowspan=2 | rowspan=4 | 3| rowspan=4 | Elected in 1901.Retired.| rowspan=4 nowrap | Mar 4, 1901 –
Mar 3, 1907| rowspan=4 | Democratic| rowspan=4 align=right |
William Clark! rowspan=4 | 3
|- style="height:2em"! rowspan=2 | 4| rowspan=2 align=left |
Paris Gibson| rowspan=2 | Democratic| rowspan=2 nowrap | Mar 7, 1901 –
Mar 3, 1905| rowspan=2 | Elected to finish Clark's term.[2] [3] Retired.
|- style="height:2em"|
|- style="height:2em"! rowspan=3 | 5| rowspan=3 align=left |
Thomas H. Carter| rowspan=3 | Republican| rowspan=3 nowrap | Mar 4, 1905 –
Mar 3, 1911| rowspan=3 | Elected Jan 16, 1905.[4] Lost re-election.| rowspan=3 | 4|
|- style="height:2em"| | rowspan=3 | 4| rowspan=3 | Elected Jan 16, 1907.[5] Lost re-election as a Progressive.| rowspan=3 nowrap | Mar 4, 1907 –
Mar 3, 1913| rowspan=3 | Republican| rowspan=3 align=right |
Joseph M. Dixon! rowspan=3 | 4
|- style="height:2em"|
|- style="height:2em"! rowspan=6 | 6| rowspan=6 align=left |
Henry L. Myers| rowspan=6 | Democratic| rowspan=6 nowrap | Mar 4, 1911 –
Mar 3, 1923| rowspan=3 | Elected Mar 2, 1911.| rowspan=3 | 5|
|- style="height:2em"| | rowspan=3 | 5| rowspan=3 | Elected Jan 14, 1913.| rowspan=10 nowrap | Mar 4, 1913 –
Mar 2, 1933| rowspan=10 | Democratic| rowspan=10 align=right |
Thomas J. Walsh! rowspan=10 | 5
|- style="height:2em"|
|- style="height:2em"| rowspan=3 | Re-elected in 1916.Retired.| rowspan=3 | 6|
|- style="height:2em"| | rowspan=3 | 6| rowspan=3 | Re-elected in 1918.
|- style="height:2em"|
|- style="height:2em"! rowspan=15 | 7| rowspan=15 align=left |
Burton K. Wheeler| rowspan=15 | Democratic| rowspan=15 nowrap | Mar 4, 1923 –
Jan 3, 1947| rowspan=3 | Elected in 1922.| rowspan=3 | 7|
|- style="height:2em"| | rowspan=3 | 7| rowspan=3 | Re-elected in 1924.
|- style="height:2em"|
|- style="height:2em"| rowspan=6 | Re-elected in 1928.| rowspan=6 | 8|
|- style="height:2em"| rowspan=2 | rowspan=6 | 8| Re-elected in 1930.Died.[6]
|- style="height:2em"| rowspan=2 | | rowspan=2 nowrap | Mar 2, 1933 –
Mar 13, 1933| rowspan=2 colspan=3 | Vacant
|- style="height:2em"| rowspan=3
|- style="height:2em"| Appointed to continue Walsh's term.Lost nomination to finish Walsh's term.| nowrap | Mar 13, 1933 –
Nov 6, 1934| | Democratic| align=right |
John E. Erickson! 6
|- style="height:2em"| rowspan=2 | Elected to finish Walsh's term.[7] | rowspan=14 nowrap | Nov 7, 1934 –
Jan 3, 1961| rowspan=14 | Democratic| rowspan=14 align=right |
James E. Murray! rowspan=14 | 7
|- style="height:2em"| rowspan=3 | Re-elected in 1934.| rowspan=3 | 9|
|- style="height:2em"| | rowspan=3 | 9| rowspan=3 | Re-elected in 1936.
|- style="height:2em"|
|- style="height:2em"| rowspan=3 | Re-elected in 1940.Lost renomination.| rowspan=3 | 10|
|- style="height:2em"| | rowspan=3 | 10| rowspan=3 | Re-elected in 1942.
|- style="height:2em"|
|- style="height:2em"! rowspan=3 | 8| rowspan=3 align=left |
Zales Ecton| rowspan=3 | Republican| rowspan=3 nowrap | Jan 3, 1947 –
Jan 3, 1953| rowspan=3 | Elected in 1946.Lost re-election.| rowspan=3 | 11|
|- style="height:2em"| | rowspan=3 | 11| rowspan=3 | Re-elected in 1948.
|- style="height:2em"|
|- style="height:2em"! rowspan=12 | 9| rowspan=12 align=left |
Mike Mansfield| rowspan=12 | Democratic| rowspan=12 nowrap | Jan 3, 1953 –
Jan 3, 1977| rowspan=3 | Elected in 1952.[8] | rowspan=3 | 12|
|- style="height:2em"| | rowspan=3 | 12| rowspan=3 | Re-elected in 1954.Retired.
|- style="height:2em"|
|- style="height:2em"| rowspan=3 | Re-elected in 1958.| rowspan=3 | 13|
|- style="height:2em"| | rowspan=3 | 13| rowspan=3 | Elected in 1960.[9] | rowspan=9 nowrap | Jan 3, 1961 –
Jan 12, 1978| rowspan=9 | Democratic| rowspan=9 align=right |
Lee Metcalf! rowspan=9 | 8
|- style="height:2em"|
|- style="height:2em"| rowspan=3 | Re-elected in 1964.| rowspan=3 | 14|
|- style="height:2em"| | rowspan=3 | 14| rowspan=3 | Re-elected in 1966.
|- style="height:2em"|
|- style="height:2em"| rowspan=3 | Re-elected in 1970.Retired.| rowspan=3 | 15|
|- style="height:2em"| | rowspan=7 | 15| rowspan=3 | Re-elected in 1972.Died.
|- style="height:2em"|
|- style="height:2em"! rowspan=10 | 10| rowspan=10 align=left |
John Melcher| rowspan=10 | Democratic| rowspan=10 nowrap | Jan 3, 1977 –
Jan 3, 1989| rowspan=7 | Elected in 1976.| rowspan=7 | 16| rowspan=5
|- style="height:2em"| | nowrap | Jan 12, 1978 –
Jan 22, 1978| colspan=3 | Vacant
|- style="height:2em"| Appointed to finish Metcalf's term.Lost nomination to full term.Resigned early to give successor preferential seniority.| nowrap | Jan 22, 1978 –
Dec 14, 1978| | Democratic| align=right |
Paul G. Hatfield! 9
|- style="height:2em"| | nowrap | Dec 14, 1978 –
Dec 15, 1978| colspan=3 | Vacant
|- style="height:2em"| Appointed early to finish Metcalf's term, having already been elected to the next term.[10] | rowspan=19 nowrap | Dec 15, 1978 –
Feb 6, 2014| rowspan=19 | Democratic| rowspan=19 align=right |
Max Baucus! rowspan=19 | 10
|- style="height:2em"| | rowspan=3 | 16| rowspan=3 | Elected in 1978.
|- style="height:2em"|
|- style="height:2em"| rowspan=3 | Re-elected in 1982.Lost re-election.| rowspan=3 | 17|
|- style="height:2em"| | rowspan=3 | 17| rowspan=3 | Re-elected in 1984.
|- style="height:2em"|
|- style="height:2em"! rowspan=9 | 11| rowspan=9 align=left |
Conrad Burns| rowspan=9 | Republican| rowspan=9 nowrap | Jan 3, 1989 –
Jan 3, 2007| rowspan=3 | Elected in 1988.| rowspan=3 | 18|
|- style="height:2em"| | rowspan=3 | 18| rowspan=3 | Re-elected in 1990.
|- style="height:2em"|
|- style="height:2em"| rowspan=3 | Re-elected in 1994.| rowspan=3 | 19|
|- style="height:2em"| | rowspan=3 | 19| rowspan=3 | Re-elected in 1996.
|- style="height:2em"|
|- style="height:2em"| rowspan=3 | Re-elected in 2000.Lost re-election.| rowspan=3 | 20|
|- style="height:2em"| | rowspan=3 | 20| rowspan=3 | Re-elected in 2002.
|- style="height:2em"|
|- style="height:2em"! rowspan=11 | 12| rowspan=11 align=left |
Jon Tester| rowspan=11 | Democratic| rowspan=11 nowrap | Jan 3, 2007 –
present| rowspan=3 | Elected in 2006.| rowspan=3 | 21|
|- style="height:2em"| | rowspan=5 | 21| rowspan=3 | Re-elected in 2008.Announced retirement, then resigned to become U.S. Ambassador to China.
|- style="height:2em"|
|- style="height:2em"| rowspan=5 | Re-elected in 2012.| rowspan=5 | 22| rowspan=3
|- style="height:2em"| | nowrap | Feb 6, 2014 –
Feb 9, 2014| colspan=3 | Vacant
|- style="height:2em"| Appointed to finish Baucus's term.Ran for election to full term, but withdrew.| nowrap | Feb 9, 2014 –
Jan 3, 2015| | Democratic| align=right |
John Walsh! 11
|- style="height:2em"| | rowspan=3 | 22| rowspan=3 | Elected in 2014.| rowspan=6 nowrap | Jan 3, 2015 –
present| rowspan=6 | Republican| rowspan=6 align=right |
Steve Daines! rowspan=6 | 12
|- style="height:2em"|
|- style="height:2em"| rowspan=3 | Re-elected in 2018.| rowspan=3 | 23|
|- style="height:2em"| | rowspan=3 | 23| rowspan=3 |Re-elected in 2020.
|- style="height:2em"|
|- style="height:2em"| rowspan=2 colspan=5 | To be determined in the 2024 election.| rowspan=2|24|
|- style="height:2em"| | 24| colspan=5 | To be determined in the 2026 election.