"I return to the White House more determined and more inspired than ever about the work there is to do and the future that lies ahead," a hoarse Obama told an enthusiastic crowd at his headquarters in Chicago early Wednesday. "Tonight you voted for action, not politics as usual."
Obama promised to work with Democrats and Republicans to quickly address the challenges facing the country because the America "voted for action."
He said he would contact Republican rival Mitt Romney to "talk about where we can work together to move this country forward."
"This country has more wealth than any nation, but that's not what makes us rich. We have the most powerful military in history, but that's not what makes us strong. Our university, our culture are all the envy of the world, but that's not what keeps the world coming to our shores," he told an enthusiastic crowd estimated at 10,000 people.
"What makes America exceptional are the bonds that hold together the most diverse nation on Earth," he said.
He said he looked forward to reaching out and working with leaders of both parties "to meet the challenges we can only solve together," such as reducing the deficit, reforming the tax code, reforming the immigration system and freeing the country from foreign oil.
"We've got more work to do," he said.
He said he believes the country "can seize this future together because we are not as divided as our politics suggests. We're not as cynical as the pundits believe. We are greater than the sum of our individual ambitions, and we remain more than a collection of red states and blue states. We are and forever will be the United States of America."
Romney conceded the election to Obama, saying early Wednesday he prayed the president succeeds in leading the nation for four years.
"This is a time of great challenges for America," Romney said. "And I pray the president is successful in guiding our nation."
Romney said the country was at a "critical point" and "can't risk partisan bickering."
Obama, he said, "must reach across the aisle to do the people's work."
Governments at all levels, he said, must "put the people before the politics."
"I believe in America; I believe in the people in America," Romney said. "I ran for office because I'm concerned about America."
Romney said he and running mate Paul Ryan "left everything on the field ... but the nation chose another leader."
In states considered both camps considered must-win, networks projected Obama the winner in Pennsylvania, Ohio, Iowa, Nevada, Wisconsin, Michigan, Colorado, Virginia and Minnesota.
Romney picked up North Carolina, a battleground state that was in Obama's column in 2008.
Florida, with its 29 electoral votes, had not been called by 3 a.m.
Obama had a projected 303 electoral votes and Romney had 206 electoral votes. A candidate needs 270 electoral votes to win the presidency.
In the popular vote, Obama had 57,374,701 votes to Romney's 55,594,273 votes, for a 50 percent to 48 percent edge.
Of the typically red states Obama won in 2008, Romney flipped two -- North Carolina and Indiana.
The road to the White House was pocked with some bitter campaigning on both sides, as each candidate accused the other of not having a plan to lead the country for the next four years. Romney jumped on the economic malaise and high unemployment, touting his business acumen. Obama asked voters to give him another four years to help nurture the slowly recovering economy.
Since the American people re-elected Obama and re-elected a GOP majority in the House, "if there is a mandate, it is a mandate for both parties to find common ground and take steps together to help our economy grow and create jobs," House Speaker John Boehner said in a statement.
Senate Minority Leader Mitch McConnell, R-Ky., however, was more blunt, The (Louisville) Courier Journal reported.
"The voters have not endorsed the failures or excesses of the president's first term, they have simply given him more time to finish the job they asked him to do together with a Congress that restored balance to Washington after two years of one-party control," McConnell said in a statement. "Now it's time for the president to propose solutions that actually have a chance of passing the Republican-controlled House of Representatives and a closely divided Senate, step up to the plate on the challenges of the moment, and deliver in a way that he did not in his first four years in office."