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"We're all in this together. That's how we campaigned, and that's who we are. Thank you," Mr. Obama tweeted, as celebrations erupted in his home town of Chicago, while challenger Mitt Romney's Boston headquarters went quiet.
As Mr. Obama began to break away from a tight race, it was the pivotal state of Ohio that put him over the 270 electoral votes needed to clinch the presidency.
"A long campaign is now over and whether I earned your vote or not, I have listened to you, I have learned from you, and you have made me a better president," Mr. Obama told a crowd of cheering supporters during his victory speech in Chicago.
Watch President Obama deliver his victory speech
The president thanked Romney for a competitive contest and congratulated him on his family's legacy of public service, adding that he wants to meet with Romney to discuss how to work together.
He added that he would return to the White House more determined and more inspired than ever.
Romney told a crowd of his supporters in Boston that he called President Obama to congratulate him on the victory.
Watch Mitt Romney deliver his concession speech
"I pray that the president will be successful in guiding our nation," Romney said.
Romney told the crowd that his wife, Ann, would have made a great first lady. He also thanked his supporters and running mate, Paul Ryan, saying the Wisconsin congressman had a bright future in the GOP.
ABC News projects President Obama has 303 electoral votes and Romney has 206. Florida was the lone state to have a race too close to call.
States called for Mr. Obama:
- California (55 electoral votes)
- Colorado (9 electoral votes)
- Connecticut (7 electoral votes)
- Delaware (3 electoral votes)
- Hawaii (4 electoral votes)
- Illinois (20 electoral votes)
- Iowa (6 electoral votes)
- Maine (4 electoral votes)
- Maryland (10 electoral votes)
- Massachusetts (11 electoral votes)
- Michigan (16 electoral votes)
- Minnesota (10 electoral votes)
- Nevada (6 electoral votes)
- New Hampshire (4 electoral votes)
- New Jersey (14 electoral votes)
- New Mexico (5 electoral votes)
- New York (29 electoral votes)
- Ohio (18 electoral votes)
- Oregon (7 electoral votes)
- Pennsylvania (20 electoral votes)
- Rhode Island (4 electoral votes)
- Vermont (3 electoral votes)
- Virginia (13 electoral votes)
- Washington (12 electoral votes)
- Washington, D.C. (3 electoral votes)
- Wisconsin (10 electoral votes)
States called for Romney:
- Alabama (9 electoral votes)
- Alaska (3 electoral votes)
- Arizona (11 electoral votes)
- Arkansas (6 electoral votes)
- Georgia (16 electoral votes)
- Idaho (4 electoral votes)
- Indiana (11 electoral votes)
- Kansas (6 electoral votes)
- Kentucky (8 electoral votes)
- Louisiana (8 electoral votes)
- Mississippi (6 electoral votes)
- Missouri (10 electoral votes)
- Montana (3 electoral votes)
- Nebraska (5 electoral votes)
- North Carolina (15 electoral votes)
- North Dakota (3 electoral votes)
- Oklahoma (7 electoral votes)
- South Carolina (9 electoral votes)
- South Dakota (3 electoral votes)
- Tennessee (11 electoral votes)
- Texas (38 electoral votes)
- Utah (6 electoral votes)
- West Virginia (5 electoral votes)
- Wyoming (3 electoral votes
The first Election Day votes came in at midnight, with the New Hampshire villages of Dixville Notch and Hart's Location maintaining their tradition of heading to the polls first. In Dixville Notch, the numbers were five votes apiece for Mr. Obama and Romney after 43 seconds of voting. In Hart's Location, it took voters 5 minutes and 42 seconds to cast 23 votes for Mr. Obama, 9 for Romney and 1 for Libertarian Gary Johnson.
Subscribe to ABC7 reporter Elex Michaelson on Facebook or follow him on Twitter for live updates from the Obama campaign headquarters in Chicago
Romney campaign officials said he voted in his home town of Belmont, Mass. Romney visited campaign offices in Ohio and Pennsylvania on Tuesday, before heading to Boston to await election returns.
Mr. Obama voted early in-person on Oct. 25. On Election Day, he did some light campaigning, but for the most part spent the day with his family in Chicago and also played a pick-up basketball game, as he did in 2008.
Subscribe to ABC7 reporter Carlos Granda on Facebook or follow him on Twitter for live updates from the Romney campaign headquarters Boston
In winning a re-election, President Obama is tasked with improving an economy burdened by high unemployment, stagnant pay, a European financial crisis, slowing global growth and U.S. companies still too anxious to expand much, among other issues.
Even before Mr. Obama gets to his second inaugural on Jan. 20, he must deal with the threatened "fiscal cliff." A combination of automatic tax increases and steep across-the-board spending cuts are set to take effect in January if Washington doesn't quickly reach a budget deal. Experts have warned that the economy could tip back into recession without an agreement.
Newly elected Democrats signaled they want compromise the avoid the fiscal cliff.
The president has said he would help create jobs by preserving low income tax rates for all except high-income Americans, spending more on public works and giving targeted tax breaks to businesses.
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The jobs picture has already been improving gradually. Employers added a solid 171,000 jobs in October. Hiring was also stronger in August and September than first thought.
ABC News and the Associated Press contributed to this report.
