| Election Name: | 2004 United States Senate elections |
| Country: | United States |
| Type: | legislative |
| Ongoing: | no |
| Previous Election: | 2002 United States Senate elections |
| Previous Year: | 2002 |
| Next Election: | 2006 United States Senate elections |
| Next Year: | 2006 |
| Majority Seats: | 51 |
| Election Date: | November 2, 2004 |
| 1Blank: | Seats up |
| 2Blank: | Races won |
| Party1: | Republican Party (US) |
| Image1: | Bill Frist official photo (3x4b).jpg |
| Leader Since1: | January 3, 2003 |
| Seats Before1: | 51 |
| Seats After1: | 55 |
| Seat Change1: | 4 |
| Popular Vote1: | 39,920,562 |
| Percentage1: | 45.3% |
| 1Data1: | 15 |
| 2Data1: | 19 |
| Party2: | Democratic Party (US) |
| Leader2: | Tom Daschle (Lost re-election) |
| Leader Since2: | January 3, 1995 |
| Seats Before2: | 48 |
| Seats After2: | 44 |
| Seat Change2: | 4 |
| Popular Vote2: | 44,754,618 |
| Percentage2: | 50.8% |
| 1Data2: | 19 |
| 2Data2: | 15 |
| Party4: | Independent |
| Seats Before4: | 1[1] |
| Seats After4: | 1 |
| Popular Vote4: | 186,231 |
| Percentage4: | 0.2% |
| 1Data4: | 0 |
| 2Data4: | 0 |
| Map Size: | 320px |
| Before Party: | Republican Party (US) |
| After Party: | Republican Party (US) |
The 2004 United States Senate elections were held on November 2, 2004, with all Class 3 Senate seats being contested. They coincided with the re-election of George W. Bush as president and the United States House elections, as well as many state and local elections. Senators who were elected in 1998, known as Senate Class 3, were seeking re-election or retiring in 2004.
Republicans won 6 seats but lost two themselves, giving them a net gain of four seats. 5 of the 6 gains came from Southern states. Conservative Democrat Zell Miller of Georgia, who campaigned for President Bush, chose not to run for re-election and Republican Johnny Isakson won his seat; Democrat Fritz Hollings of South Carolina chose not to run for re-election and was succeeded by Republican Jim DeMint; Democratic vice presidential nominee John Edwards chose not to run for re-election and Republican Richard Burr won his North Carolina seat; Democrat Bob Graham of Florida chose not to run for re-election, and his seat went to Republican Mel Martinez; and Louisiana Democrat John Breaux chose not to run for re-election and Republican David Vitter won his seat.
In South Dakota, Republican John Thune defeated the incumbent Senate minority leader Tom Daschle, marking the first and only time since 1952 that a sitting party leader lost re-election, as well as the only time that person was the minority leader. Republican Senator Peter Fitzgerald of Illinois chose not to run for re-election and Democrat Barack Obama won in a landslide, becoming the Senate's only black member and only the third popularly elected in American history and only the third elected since Reconstruction. Also, Republican Senator Ben Nighthorse Campbell of Colorado chose not to run for re-election and Democrat Ken Salazar won the open seat.
This was the third consecutive election cycle for Senate Class 3 where the Democrats either broke even or lost seats. This also marked the first time since 1980 in which a presidential candidate from either party won with coattails in the Senate., these are the last elections held during a presidential election year in which the Republicans made a net gain of seats. Barack Obama, the 44th President of the United States, was first elected to the Senate from Illinois in this election.
| 44 | 1 | 55 |
| Democratic | Independent | Republican |
| Parties | Total | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Democratic | Republican | Independent | Libertarian | Others | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Before these elections | 48 | 51 | 1 | — | — | 100 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| End of this Congress (two months later) | 48 | 51 | 1 | — | — | 100 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Not Up | 29 | 36 | 1 | — | — | 66 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Up | 19 | 15 | — | — | — | 34 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Incumbent retired | Total before | 5 | 3 | — | — | — | 8 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Held by same party | — | 1 | — | — | — | 1 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Replaced by other party | 2 Republicans replaced by 2 Democrats 5 Democrats replaced by 5 Republicans | — | — | — | 7 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Result after | 2 | 6 | — | — | — | 8 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Incumbent ran | Total before | 14 | 12 | — | — | — | 26 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Won re-election | 13 | 12 | — | — | — | 25 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Lost re-election | 1 Democrat replaced by 1 Republican | — | — | — | 1 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Lost renomination, held by same party | — | — | — | — | — | 0 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Lost renomination, and party lost | — | — | — | — | — | 0 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Result after | 13 | 13 | — | — | — | 26 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Net gain/loss | 4 | 4 | — | — | — | 4 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Total elected | 15 | 19 | — | — | — | 34 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Result | 44 | 55 | 1 | — | — | 100 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Popular vote | Votes | 44,754,618 | 39,920,562 | 186,231 | 754,861 | 2,481,075 | 88,097,347 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Share | 50.80% | 45.31% | 0.21% | 0.86% | 2.82% | 100% | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||