The US president told the crowd, who chanted "four more years" as he arrived on stage, that they had "lifted me up the whole way and I will always be grateful".
And he heaped praise on his family, revealing he had never loved his wife Michelle more and commending his "smart, beautiful" daughters.
Mr Obama vowed to revive America's economy but warned "progress will come in fits and starts".
Thanking the thousands of supporters in the room, he told them: "Tonight, more than 200 years after a former colony won the right to determine its own destiny, the task of perfecting our union moves forward.
"It moves forward because of you, it moves forward because you reaffirmed the spirit that has triumphed over war and oppression, the spirit that has lifted this country from the depths of despair to the great heights of hope, the belief that while each of us will pursue our own individual dreams, we are an American family and we rise or fall together as one nation and as one people.
"Tonight, in this election, you, the American people, reminded us that while our road has been hard, while our journey has been long, we have picked ourselves up, we have fought our way back, and we know in our hearts that for the United States of America, the best is yet to come."
The president acknowledged the patience of those who had waited in lengthy queues to register their preference -- telling them whether they were Obama or Romney voters, they had made a difference.
Mr Obama said he had congratulated Mr Romney and his running mate Paul Ryan on what he called a "hard-fought campaign", saying that they had battled each other fiercely because they cared so much about the future of their country.
In a speech lasting almost 25 minutes, Mr Obama insisted he had hope for the future but admitted there was "more work to do".
"The best is yet to come, but we have more work to do," he told the crowd.
He said his supporters "voted for action, not business as usual" as he vowed to reduce the deficit, reform taxation and fix the immigration system.
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