The 2008 United States Senate elections were held on November 4, 2008, with 35 of the 100 seats in the Senate being contested. 33 seats were up for regular elections; the winners were eligible to serve 6-year terms from January 3, 2009, to January 3, 2015, as members of Class 2. There were also 2 special elections, the winners of those seats would finish the terms that ended on January 3, 2013. The presidential election, which was won by Democrat Barack Obama, elections for all House of Representatives seats; elections for several gubernatorial elections; and many state and local elections occurred on the same date.

Going into these elections, the Senate consisted of 49 Democrats, 49 Republicans, and 2 Independents who caucused with the Democrats, giving the Democratic caucus the slightest 51–49 majority. Of the seats up for election in 2008, 23 were held by Republicans and 12 by Democrats. The Republicans, who openly conceded early on that they would not be able to regain the majority in this election, lost 8 seats. Democratic candidates defeated Republican incumbents in Alaska, New Hampshire, North Carolina, Oregon, and, after a lengthy recount process, Minnesota. Additionally, they won Republican-held open seats in Colorado, New Mexico, and Virginia.

Each major party has Hill committees that work to support its candidates for the House and Senate, chiefly by providing funds. On the Senate side, the committees are the Democratic Senatorial Campaign Committee (DSCC) and the National Republican Senatorial Committee (NRSC). In this cycle, the DSCC was more successful at fundraising. As of June 30, 2008, data from the Federal Election Commission showed the NRSC with $24.6 million on hand, as compared with the DSCC's $43 million. The NRSC chair, senator John Ensign, took the unusual step of chastising the Republican Senators who, like him, were not facing re-election, and who he thought should have done more to help raise money for their colleagues.

This election cycle was the second cycle in a row in which no seats switched from Democratic to Republican, and the first since 1990 in which the Democrats retained all their seats. In addition, this was the largest Democratic Senate gain since 1986, where they also won 8 seats. These elections marked the first time since 1964 in which a Democratic presidential candidate who won the White House had a Senate coattail effect. As of 2024, this is the last time Democrats won U.S. Senate seats in Alaska, Arkansas, Iowa, Louisiana, North Carolina, and South Dakota.

As of 2025, this is the most recent time in which the Democratic Party won a majority of Class 2 Senate seats in a regularly scheduled election.

Along with 2 independents who caucus with them, Democrats held at least 58 seats as a result of the elections. The April 2009 party switch of Pennsylvania senator Arlen Specter from Republican to Democrat and the July 2009 resolution of the Minnesota election in favor of Democrat Al Franken increased the Democratic majority to 60–40 (briefly providing the Democrats a filibuster-proof majority, and thus they were able to hypothetically override any filibusters). Republicans gained a seat in a January 2010 special election in Massachusetts, thereby making the balance 59–41 before the start of the next election cycle.

Results summary + ↓ 57 2 41 Democratic Independent Republican Summary of the 2008 United States Senate elections results Parties Total Democratic Republican Independent Libertarian Independence Green Others Before these elections 49 49 2 — — — — 100 Notup 22 8 2 — — — — 31 15 19 — — — — — 34 Total 37 26 2 — — — — 65 Up — 2 — — — — — 2 12 21 — — — — — 33 Total 12 23 — — — — — 35 Incumbentretired Total before — 5 — — — — — 5 — 2 — — — — — 2 3 Republicansreplaced by 3 Democrats — — — — — 3 Result after 3 2 — — — — — 5 Incumbentran Total before 12 18 — — — — — 30 12 13 — — — — — 25 5 Republicansreplaced by 5 Democrats — — — — — 5 Result after 17 13 — — — — — 30 Net gain/loss 8 8 — — — — — 8 Total elected 20 15 — — — — — 35 Nation-wide vote VotesFor the Georgia senate race, votes from the runoff election are counted. 33,650,061 28,863,067 176,752 798,154 450,702 427,427 496,124 64,862,287 Share 51.88% 44.50% 0.27% 1.23% 0.69% 0.66% 0.76% 100% Result 57 41 2 — — — — 100

Sources: Clerk of the U.S. House of Representatives U.S. Senate Popular Vote and FEC Total Receipts by Party, via TheGreenPapers.com

Change in composition

Before the elections D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D I Majority (with Independents) ↑ I R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R

After the elections D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D Majority → D R Vacant I I D D D D D R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R

Beginning of the first session D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D Majority → D I I D D D D D D D R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R

Key: D Democratic I Independent R Republican

Race summary

Special elections during the 110th Congress In these special elections, the winner was seated during 2008 or before January 3, 2009, sorted by election date, then state, then class.

State Incumbent Results Candidates Senator Party Electoral history Mississippi(Class 1) Republican 2007 Interim appointee elected. Wyoming(Class 1) Republican 2007 Interim appointee elected.

Elections leading to the next Congress In these general elections, the winners were elected for the term beginning January 3, 2009; ordered by state.

All of the elections involved the Class 2 seats.

State Incumbent Results Candidates Senator Party Electoral history Alabama Republican 19962002 Incumbent re-elected. Alaska Republican 1968 1970 (special)197219781984199019962002 Incumbent lost re-election.Democratic gain. Arkansas Democratic 2002 Incumbent re-elected. Colorado Republican 19962002 Incumbent retired.Democratic gain. Delaware Democratic 197219781984199019962002 Incumbent re-elected. Georgia Republican 2002 Incumbent re-elected in runoff. Idaho Republican 199019962002 Incumbent retired.Republican hold. Illinois Democratic 19962002 Incumbent re-elected. Iowa Democratic 1984199019962002 Incumbent re-elected. Kansas Republican 19962002 Incumbent re-elected. Kentucky Republican 1984199019962002 Incumbent re-elected. Louisiana Democratic 19962002 Incumbent re-elected. Maine Republican 19962002 Incumbent re-elected. Massachusetts Democratic 1984199019962002 Incumbent re-elected. Michigan Democratic 19781984199019962002 Incumbent re-elected. Minnesota Republican 2002 Incumbent lost re-election.Democratic (DFL) gain.Winner delayed term until July 7, 2009, due to election dispute. Mississippi Republican 19781984199019962002 Incumbent re-elected. Montana Democratic 19781984199019962002 Incumbent re-elected. Nebraska Republican 19962002 Incumbent retired.Republican hold. New Hampshire Republican 2002 Incumbent lost re-election.Democratic gain. New Jersey Democratic 19821982 198819942000 2002 Incumbent re-elected. New Mexico Republican 197219781984199019962002 Incumbent retired.Democratic gain. North Carolina Republican 2002 Incumbent lost re-election.Democratic gain. Oklahoma Republican 1994 19962002 Incumbent re-elected. Oregon Republican 19962002 Incumbent lost re-election.Democratic gain. Rhode Island Democratic 19962002 Incumbent re-elected. South Carolina Republican 2002 Incumbent re-elected. South Dakota Democratic 19962002 Incumbent re-elected. Tennessee Republican 2002 Incumbent re-elected. Texas Republican 20022002 Incumbent re-elected. Virginia Republican 19781984199019962002 Incumbent retired.Democratic gain. West Virginia Democratic 1984199019962002 Incumbent re-elected. Wyoming Republican 19962002 Incumbent re-elected.

Special elections during the next Congress There were no special elections in 2009.

Closest races In nine races the margin of victory was under 10%. However, Georgia proceeded to a runoff election where the Republican candidate won by over 10%.

District Winner Margin Minnesota Democratic (flip) 0.01% Alaska Democratic (flip) 1.3% Oregon Democratic (flip) 3.6% Georgia general Republican 3.0% Kentucky Republican 5.9% New Hampshire Democratic (flip) 6.3% Louisiana Democratic 6.4% North Carolina Democratic (flip) 8.5% Mississippi special Republican 9.9%

South Dakota was the tipping point state, decided by a margin of 25.0%.

Final pre-election predictions Several sites and individuals published predictions of competitive seats. These predictions looked at factors such as the strength of the incumbent (if the incumbent was running for re-election) and the other candidates, and the state's partisan lean (reflected in part by the state's Cook Partisan Voting Index rating). The predictions assigned ratings to each seat, indicating the predicted advantage that a party had in winning that seat. Most election predictors used: "tossup": no advantage "tilt" (used by some predictors): advantage that is not quite as strong as "lean" "lean": slight advantage "likely": significant, but surmountable, advantage "safe" or "solid": near-certain chance of victory Constituency Incumbent 2008 election ratings State Senator LastelectionCookCQ PoliticsRace Ratings Chart: Senate CQ PoliticsRothenbergRCPResult Alabama Jeff Sessions 58.6% R Sessions(63.4%) Alaska Ted Stevens 78.2% R Begich(47.8%) Arkansas Mark Pryor 53.9% D Pryor (79.5%) Colorado Wayne Allard 50.7% R M. Udall(52.8%) Delaware Joe Biden 58.2% D Biden (64.7%) Georgia Saxby Chambliss 52.8% R Chambliss(57.4%) Idaho Larry Craig 65.2% R Risch(57.7%) Illinois Dick Durbin 60.3% D Durbin(67.8%) Iowa Tom Harkin 54.2% D Harkin(62.7%) Kansas Pat Roberts 82.5% R Roberts (60.1%) Kentucky Mitch McConnell 64.7% R McConnell(53.0%) Louisiana Mary Landrieu 51.7% D Landrieu(52.1%) Maine Susan Collins 58.4% R Collins(61.3%) Massachusetts John Kerry 80.0% D Kerry(65.9%) Michigan Carl Levin 60.6% D Levin (62.7%) Minnesota Norm Coleman 49.5% R Franken (42.0%) Mississippi (regular) Thad Cochran 84.6% R Cochran(61.4%) Mississippi (special) Roger Wicker Appointed Wicker(55.0%) Montana Max Baucus 62.7% D Baucus (72.9%) Nebraska Chuck Hagel 82.8% R Johanns(57.5%) New Hampshire John Sununu 50.8% R Shaheen(51.6%) New Jersey Frank Lautenberg 53.9% D Lautenberg(56.0%) New Mexico Pete Domenici 65.0% R T. Udall(61.3%) North Carolina Elizabeth Dole 53.5% R Hagan(52.6%) Oklahoma Jim Inhofe 57.3% R Inhofe(56.7%) Oregon Gordon Smith 56.2% R Merkley(48.9%) Rhode Island Jack Reed 78.4% D Reed(73.4%) South Carolina Lindsey Graham 54.4% R Graham(57.5%) South Dakota Tim Johnson 49.6% D Johnson (62.5%) Tennessee Lamar Alexander 54.3% R Alexander (65.1%) Texas John Cornyn 55.3% R Cornyn(54.8%) Virginia John Warner 82.6% R M. Warner(65.0%) West Virginia Jay Rockefeller 63.1% D Rockefeller(63.7%) Wyoming (regular) Mike Enzi 73.0% R Enzi(75.6%) Wyoming (special) John Barrasso Appointed Barrasso (73.4%)

Gains and losses

Retirements Five Republicans retired rather than seek re-election. StateSenator Age at end of term AssumedofficeReplaced by Colorado 65 1997 Idaho 63 1991 Nebraska 62 1997 New Mexico 76 1973 Virginia 81 1979

Defeats Five Republicans sought re-election but lost in the general election. StateSenatorAge atend of termAssumedofficeReplaced by Alaska 85 1968 Minnesota 59 2003 New Hampshire 44 2003 North Carolina 72 2003 Oregon 56 1997

Post-election changes Four Democrats resigned and were replaced by Democrats. One Republican was switched to Democrat on April 28, 2009. Two other Democrats died on August 25, 2009, and June 28, 2010, respectively, while another Republican resigned on September 9, 2009.