He needs to work with Republicans in Congress to confront a looming "fiscal cliff" of tax rises and spending cuts. The Republicans retained control of the House of Representatives on Tuesday, but failed to take the Senate.
In his state-by-state battle with Republican Mitt Romney, Mr Obama has so far won 303 electoral college votes to Mr Romney's 206, past the 270-vote winning post. In Florida, a state with 29 electoral votes, absentee ballots are still being counted and the race remains too close to call.
Before Mr Obama's Washington return on Wednesday, House Speaker John Boehner hinted at the possibility of a compromise if the president agreed to tax reform. Mr Boehner, who negotiated with Mr Obama over a so-called "grand bargain" of spending cuts and new revenues in 2011, said he would accept new revenue-raising as part of a tax reform deal.
Time is tight: Bush-era tax cuts are due to expire at the end of 2012, and automatic, mandatory across-the-board cuts to military and domestic spending are also in the pipeline unless a deal can be reached. Economists say the overall effect of falling off the "fiscal cliff" could tip the US into recession.
In his first public remarks since the election, Mr Boehner said Republicans in the House of Representatives stood ready to work with the president on avoiding the fiscal cliff.
What is the fiscal cliff?
- Under a deal reached last year between President Obama and the Republican-controlled Congress, existing stimulus measures - mostly tax cuts - will expire on 1 January 2013
- Cuts to defence, education and other government spending will then automatically come into force - the "fiscal cliff" - unless Congress acts
- The economy does not have the momentum to absorb the shock from going over the fiscal cliff without going into recession
He said Republicans - previously strongly opposed to any new tax-related revenue - would be willing to compromise as long as the tax code was reformed and accompanied by changes to benefit programmes.
"Mr President, this is your moment. We're ready to be led, not as Democrats or Republicans, but as Americans," Mr Boehner said. "We want you to succeed."
Mr Obama's prospects for his second term will hinge on the his relationship with Mr Boehner and congressional Republicans.
Vice-President Joe Biden told reporters aboard Air Force Two that there was much work to be done.
"We're really anxious to get moving on, first of all, dealing with the first things first, this fiscal cliff. I think we can do it," Mr Biden said. But he added that negotiations would depend on how co-operative their Republican colleagues were.
Reacting to Mr Obama's win, Mitch McConnell, the Republican minority leader in the Senate, said voters had not endorsed "the failures or excesses of the president's first term", but had given him "more time to finish the job" by working with Congress.
In the president's acceptance speech at his campaign headquarters in Chicago on Tuesday night, Mr Obama also pledged to consult his campaign rival Mitt Romney and explore ways to work together.When the Republican conceded defeat with a brief speech shortly after midnight on Wednesday in Boston, Mr Romney urged both parties to "put the people before politics".
Congress returns next week to begin dealing with the fiscal cliff. The fragile economy was rated the top issue by about six out of 10 voters in Tuesday's exit polls. But most of them blamed former President George W Bush for the downturn. Economists warn that if the fiscal cliff takes effect in January, it could reduce GDP by enough to put the US back in recession in the first half of 2013.
Mr Obama was re-elected with the highest unemployment rate - at 7.9% - for any incumbent president since the US wartime leader Franklin Roosevelt.
Preliminary figures suggest fewer people voted than four years ago. With most ballots tallied, more than 117 million people participated, compared to record-breaking figures of 131 million four years ago. Turnout was down sharply in some states, including Texas, as well as states on the US East Coast that were hit hard by superstorm Sandy.
In addition to the presidential and congressional races, Americans voted on a number of state-wide legal issues.
- Referendums in Maine, Maryland and Washington state approved same-sex marriage while a measure in Minnesota to block gay unions failed
- Colorado and Washington state voted to legalise recreational use of marijuana
- California voters rejected a proposal to abolish the death penalty
- In a referendum, Puerto Ricans voted in favour of becoming the 51st US state, if Congress approves the move.