Widow Jean (left) will work for her husband's ideals
Mel Carnahan, a Democrat and former governor of Missouri State in the Mid-West, died too late for his name to be removed from the ballot.
Under state election rules he is likely to be replaced by his widow, Jean, after the narrow victory over his Republican rival by about 1% of the vote.
The plane crash that killed the governor, his son and an aide last month turned what was already a bitterly fought contest against Republican Senator John Ashcroft, into a bizarre contest.
Heirs of a dream
Jean Carnahan promised to take up her husband's seat if he was elected, in order to fight for her dead husband's ideals.
Mrs Carnahan, 66, who has never run for or held public office, compared her husband's unfinished work to that of Abraham Lincoln and Martin Luther King.
"We remain heirs of a legacy, heirs of a dream," she said.
No-one has posthumously won election to the Senate before.
Mr Carnahan and his incumbent Republican rival John Ashcroft were running neck-and-neck in a hard-fought campaign at the time of his death.
Difficult campaign
The Republicans though faced a difficult campaign against a newly-widowed woman and her popular late husband.
"How do you campaign against a ghost? There's no precedent for this," said political scientist Richard Fulton of Northwest Missouri State University.
Three widows of congressmen are currently members of the US House of Representatives - Mary Bono, a Republican, and Lois Capps, a Democrat, both from California, and Jo Ann Emerson, a Missouri Republican.
All three first won special elections to succeed their husbands, and all three won re-election in 1998.