Mr Obama captured the key battleground states of Pennsylvania and Ohio, before passing the essential figure of 270.
Republican John McCain has publicly conceded defeat.
"We have come to the end of a long journey," McCain told supporters.
"The American people have spoken and they have spoken clearly.
He said he had called Democrat Barack Obama "to congratulate him on being elected the next president of the country that we both love".
Barack Obama will be America’s 44th president after campaigning on a message of change and hope. He takes office with a trillion-dollar deficit and as commander-in-chief of a military at war in two countries.
Mr Obama is the first African-American to be nominated by a major American political party for president. A graduate of Columbia University and Harvard Law School, where he became the first black person to serve as president of the Harvard Law Review, Obama worked as a community organiser and practiced as a civil rights attorney before serving three terms in the Illinois Senate from 1997 to 2004.
He taught constitutional law at the University of Chicago Law School from 1992 to 2004. Following an unsuccessful bid for a seat in the U.S. House of Representatives in 2000, he announced his campaign for the U.S. Senate in January 2003.
After a primary victory in March 2004, Obama delivered the keynote address at the Democratic National Convention in July 2004.
He was elected to the Senate in November 2004 with 70 percent of the vote.
As a member of the Democratic minority in the 109th Congress, he helped create legislation to control conventional weapons and to promote greater public accountability in the use of federal funds. He also made official trips to Eastern Europe, the Middle East, and Africa.
During the 110th Congress, he helped create legislation regarding lobbying and electoral fraud, climate change, nuclear terrorism, and care for returned U.S. military personnel.
MrObama announced his presidential campaign in February 2007, and was formally nominated at the 2008 Democratic National Convention with Delaware senator Joe Biden as his running mate.
Want to know more?Goodbye George Obama's Kenyan relatives cheer win
Ex-classmates in Indonesia applaud Obama
Obama has realised King's dream: Rudd