The son of a black father from Kenya and a white mother from Kansas, the Democratic senator from Illinois sealed his victory by defeating Republican Sen. John McCain in a string of wins in hard-fought battleground states - Ohio, Florida, Virginia and Iowa.
A huge crowd in Grant Park in Chicago erupted in jubilation at the news of Obama's victory. Some wept.
McCain called to concede defeat - and the end of his own 10-year quest for the White House.
Obama and his running mate, Sen. Joseph Biden of Delaware, will take their oaths of office as president and vice president on Jan. 20, 2009.
As the 44th president, Obama will move into the Oval Office as leader of a country that is almost certainly in recession, and fighting two long wars, one in Iraq, the other in Afghanistan.
The popular vote was close, but not the count in the Electoral College, where it mattered most.
There, Obama's audacious decision to contest McCain in states that hadn't gone Democratic in years paid rich dividends.
Obama has said his first order of presidential business will be to tackle the economy. He has also pledged to withdraw most U.S. combat troops from Iraq within 16 months.
Fellow Democrats rode his coattails to larger majorities in both houses of Congress. They defeated incumbent Republicans and won open seats by turn.