Click to play videoBarack Obama told supporters that "change has come to America," as he addressed the country for the first time as the president-elect.
"The road ahead will be long. Our climb will be steep. We may not get there in one year or even one term, 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," Obama said in Chicago, Illinois.
Police estimated that 125,000 people gathered in Grant Park to hear Obama claim victory.
Obama said he was looking forward to working with Senator John McCain and Governor Sarah Palin "to renew this nation's promise in the months ahead."
McCain on Tuesday urged all Americans to join him in congratulating Senator Barack Obama on his projected victory in the presidential election.
"I pledge to him tonight to do all in my power to help him lead us through the many challenges we face," McCain said before his supporters in Phoenix, Arizona.
"Today, I was a candidate for the highest office in the country I love so much, and tonight, I remain her servant," he said.
McCain called Obama to congratulate him, Obama's campaign said.
Obama thanked McCain for his graciousness and said he had waged a tough race.
President Bush also called Obama to congratulate him.
Bush told Obama he was about to begin one of the great journeys of his life, and invited him to visit the White House as soon as it could be arranged, according to White House spokeswoman Dana Perino.
With his projected win, Obama will become the nation's 44th president and its first African-American leader.
Supporters in Chicago cheering, "Yes, we can" were met with cries of "Yes, we did."
The original Obama supporter, the queen of American television, Oprah Winfrey says the victory is bigger than the winner.
“It feels like hope won. It feels like its not just a victory for, obviously, Barack Obama. It feels like America did the right thing. It fees like there's a shift in conciseness. It feels like something big and bold happened here,” says Oprah Winfrey
More than 1,000 people gathered outside of the White House, chanting, "Obama, Obama!"
Obama's former rival for the Democratic nomination, Sen. Hillary Clinton said in a statement that "we are celebrating an historic victory for the American people."
"This was a long and hard fought campaign but the result was well worth the wait. Together, under the leadership of President Barack Obama, Vice President Joe Biden, and a Democratic Congress, we will chart a better course to build a new economy and rebuild our leadership in the world."
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