Pressing business came at him fast, with just 76 days until his inauguration as the 44th president.
The nation's top intelligence officials planned to give him top-secret daily briefings starting Thursday, sharing with him the most critical overnight intelligence as well as other information he has not been allowed to see as a senator or candidate. And Obama planned to give the first of his daily briefings to the media on Thursday as he moves quickly to begin assembling a White House staff and selecting Cabinet nominees.
Obama was asking Illinois Rep. Rahm Emanual, former political and policy adviser to President Clinton, to be his White House chief of staff, Democratic officials said. John Podesta, who served as Clinton's chief of staff, was expected to join Obama Senate aide Pete Rouse and campaign adviser Valerie Jarrett in leading the transition team.
President Bush pledged "complete cooperation" in the transition and called Obama's victory a "triumph of the American story."
Naming the staggering list of problems he inherits in his decisive defeat of Republican John McCain - two wars and "the worst financial crisis in a century," among them - Obama sought to restrain the soaring expectations of his supporters late Tuesday night even as he stoked them with impassioned calls for national unity and partisan healing.
"We may not get there in one year or even in one term," he said. "But, America, I have never been more hopeful than I am tonight that we will get there. I promise you, we as a people will get there."
Helping him to get there will be a strengthened Democratic majority in both houses of Congress. When Obama becomes the president on Jan. 20, with Delaware Sen. Joe Biden as his vice president, Democrats will control both the White House and Congress for the first time since 1994.
A tide of international goodwill came Obama's way on Wednesday morning, even as developments made clear how heavy a weight will soon be on his shoulders.
Russian President Dmitry Medvedev issued a congratulatory telegram saying there is "solid positive potential" for the election to improve strained relations between Washington and Moscow, if Obama engages in constructive dialogue.
Yet he appeared to be deliberately provocative hours after the election with sharp criticism of the U.S. and his announcement that Russia will deploy missiles near NATO member Poland in response to U.S. missile defense plans.
In Afghanistan, where villagers said the U.S. bombed a wedding party and killed 37 people, President Hamid Karzai said: "This is my first demand of the new president of the United States - to put an end to civilian casualties."
Young and charismatic but with little experience on the national level or as an executive, Obama easily defeated McCain, smashing records and remaking history along the way.
Ending an improbable journey that started for Obama a long 21 months ago, he drew a record-breaking $700 million to his campaign account alone. The first African-American destined to sit in the Oval Office, he also was the first Democrat to receive more than 50 percent of the popular vote since Jimmy Carter in 1976. He is the first senator elected to the White House since John F. Kennedy in 1960.
And Obama scored an Electoral College landslide that redrew America's political dynamics. He won states that reliably voted Republican in presidential elections, such as Indiana and Virginia, which hadn't supported a Democratic candidate in 44 years. Ohio and Florida, key to President Bush's twin victories, also went for Obama, as did Pennsylvania, which McCain had deemed crucial for his election hopes.
With most U.S. precincts tallied, the popular vote was 52.3 percent for Obama and 46.4 percent for McCain. But the count in the Electoral College was much more lopsided - 349 to 147 in Obama's favor as of early Wednesday, with three states still to be decided.
Those were North Carolina, Georgia and Missouri.
The nation awakened to the new reality at daybreak, a short night after millions witnessed Obama's election - an event so rare it could not be called a once-in-a-century happening. Prominent black leaders wept unabashedly in public, rejoicing in the elevation of one of their own, at long last.
The Rev. Jesse Jackson, who had made two White House bids himself, said on ABC's "Good Morning America" that the tears streaming down his face upon Obama's victory were about his father and grandmother and "those who paved the fights. And then that Barack's so majestic."
Rep. John Lewis, a Georgia Democrat and leading player in the civil rights movement with Jackson, said on NBC's "Today" show: "He's going to call on us, I believe, to sacrifice. We all must give up something."
Speaking from Hong Kong, retired Gen. Colin Powell, the black Republican whose endorsement of Obama symbolized the candidate's bipartisan reach and bolstered him against charges of inexperience, called the senator's victory "a very very historic occasion." But he also predicted that Obama would be "a president for all America."
On Capitol Hill, Democrats ousted incumbent GOP Sens. Elizabeth Dole of North Carolina and John Sununu of New Hampshire and captured seats held by retiring Republican senators in Virginia, New Mexico and Colorado. Still, the GOP blocked a complete rout, holding the Kentucky seat of Senate Minority Leader Mitch McConnell and a Mississippi seat once held by Trent Lott.
The Associated Press prematurely declared incumbent Sen. Norm Coleman the winner in a race against Democratic former comedian Al Franken that by state law is subject to a recount based on the 571-vote margin. The party also held onto a Mississippi seat once held by Trent Lott.
In the House, with fewer than a dozen races still undecided, Democrats captured Republican-held seats in the Northeast, South and West and were on a path to pick up as many as 20 seats.
"It is not a mandate for a party or ideology but a mandate for change," said Senate Majority Leader Harry Reid of Nevada.
After the longest and costliest campaign in U.S. history, Obama was propelled to victory by voters dismayed by eight years of Bush's presidency and deeply anxious about rising unemployment and home foreclosures and a battered stock market that has erased trillions of dollars of savings for Americans.
Six in 10 voters picked the economy as the most important issue facing the nation in an Associated Press exit poll. None of the other top issues - energy, Iraq, terrorism and health care - was selected by more than one in 10. Obama has promised to cut taxes for most Americans, get the United States out of Iraq and expand health care, including mandatory coverage for children.
McCain conceded defeat shortly after 11 p.m. EST, telling supporters outside the Arizona Biltmore Hotel, "The American people have spoken, and they have spoken clearly."
"This is an historic election, and I recognize the special significance it has for African-Americans and the special pride that must be theirs tonight," McCain said. "These are difficult times for our country. And I pledge to him tonight to do all in my power to help him lead us through the many challenges we face."
The son of a Kenyan father and a white mother from Kansas, the 47-year-old Obama has had a startlingly rapid rise, from lawyer and community organizer to state legislator and U.S. senator, now not even four years into his first term.
Almost six in 10 women supported Obama nationwide, while men leaned his way by a narrow margin, according to interviews with voters. Just over half of whites supported McCain, giving him a slim advantage in a group that Bush carried overwhelmingly in 2004.
The results of the AP survey were based on a preliminary partial sample of nearly 10,000 voters in Election Day polls and in telephone interviews over the past week for early voters.
In terms of turnout, America voted in record numbers. It looks like 136.6 million Americans will have voted for president this election, based on 88 percent of the country's precincts tallied and projections for absentee ballots, said Michael McDonald of George Mason University. Using his methods, that would give 2008 a 64.1 percent turnout rate, the highest since 65.7 percent in 1908, he said.