Incumbent Democratic Senator Chris Coons ran for re-election to a first full term in office.

He was unopposed for the Democratic nomination and defeated Republican businessman Kevin Wade in the general election.

Democratic senator Joe Biden was re-elected to a seventh term in 2008, defeating Republican political commentator Christine O'Donnell by 65% to 35%.

Delaware Governor Ruth Ann Minner appointed Biden's longtime aide Ted Kaufman to the seat until a special election was held in November 2010.

In the election, Christine O'Donnell ran again and upset U.S. Representative and former governor Mike Castle in the Republican primary to face Democrat Chris Coons, who had run unopposed for his party's nomination.