Barack Obama defeated John McCain by 6% of the popular vote, which is the exact margin predicted by YouGov's American company, YouGovPolimetrix.
Throughout the campaign, YouGovPolimetrix conducted state-by-state online polls for CBS News.
On Monday November 3, it released its final prediction based on the results of 31,148 interviews conducted online in all 50 states, plus the District of Columbia.
Excluding undecideds, YouGovPolimetrix predicted that Obama would win 52% of the national vote to John McCain's 46%, which is exactly what happened.
Six months ago, the market research company correctly predicted that Boris Johnson would defeat Ken Livingstone in the London mayoral election by 6%.
Peter Kellner, president of YouGov, said: "YouGov has long established a track record for accuracy in Great Britain. This is now extending to other countries. YouGovZapera conducted online exit polls for the Swedish general election in 2006 and the Danish general election of 2007. Both polls got the results right to within 1 point.
"With the success of YouGovPolimetrix in the United States, I believe that online research has now come of age. We are making progress towards our goal of being the world's most accurate polling company."