Democrat Cory Booker, the former mayor of Newark, won New Jersey's special election to fill Sen. Frank Lautenberg's seat for the remainder of his term.
He defeated Republican Steve Lonegan by just over 10 points.
Booker is a supporter of gay marriage in a state where the issue is the subject of a court and legislative battle.
In his victory speech, he said he is going to Washington "not to play shallow politics that's used to attack and divide but to engage in the kind of hard, humble service that reaches out to others."
Booker is the first black senator from New Jersey. He will almost immediately go back to campaigning to run for a full term in 2014.