The 2008 United States Senate election in Delaware was held on November 4, 2008. Incumbent Democratic U.S. Senator Joe Biden won re-election to a seventh term and won the Vice Presidency of the United States on the same day. Biden took his oath of office in the Senate chamber with the rest of his colleagues but resigned his seat on January 15, 2009 and assumed the Vice Presidency 5 days later.
After ending his 2008 presidential bid in January 2008, Biden focused instead on running for a seventh Senate term. He was unopposed within his party.
O'Donnell faced businessman Tim Smith at the Republican state party convention and won with more than 60 percent of the delegate vote.
On August 23, 2008, Democratic Party presidential nominee Barack Obama announced that he had selected Joe Biden to serve as his vice presidential candidate. Under Delaware law, Biden could run simultaneously for both his Senate seat and for Vice President, which Biden indeed decided to do.
The statewide party primary elections were held September 9, 2008. O'Donnell was uncontested in the Republican half, as was Biden in the Democratic.
O'Donnell tried to make an issue of Biden's dual campaigns, claiming that serving his constituents was not important to him, and criticized his unwillingness to participate in debates and candidate forums. Nevertheless, she was heavily outspent by Biden and her campaign failed to gain traction. Her campaign ended with $23,000 in debt.
Minutes after the polls closed on November 4, NBC called the race for Biden, with other news organizations soon following.