The 2008 United States Senate elections were held on November 4, 2008, with 35 of the 100 seats in the Senate being contested. Thirty-three seats were up for regular elections; the winners were eligible to serve six-year terms from January 3, 2009, to January 3, 2015, as members of Class 2. There were also two 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.

The United States Senate election in New Hampshire was held on November 4, 2008. Incumbent Republican U.S. Senator John E. Sununu ran for re-election to a second term, but was defeated by Democrat Jeanne Shaheen in a rematch of the 2002 election. Shaheen's win marked the first time since 1972 that Democrats won this seat, and made her the first Democratic Senator elected from New Hampshire since John A. Durkin's victory in 1975.