Romney said, "This election is over, but our principles endure."
Obama, meanwhile, tweeted to supporters, "This happened because of you. Thank you."
Obama was chalking up additional victories in states that the polls had said could go either way. After winning Virginia's 13 electoral votes, he had a margin of 100 electoral votes—303 to 203—with just Alaska and Florida still to count.
Florida's result remained too close to call, hours after the polls closed.
Despite Obama's sizeable margin in the electoral vote count, he held just a slim advantage in the popular vote.