"I realize that I am not the likeliest candidate for this office. I don't fit the typical pedigree, and I haven't spent my career in the halls of Washington," he said.
"But I stand before you tonight because all across America something is stirring. What the nay-sayers don't understand is that this election has never been about me. It's been about you," Obama said.
"For eighteen long months, you have stood up, one by one, and said enough to the politics of the past. You understand that in this election, the greatest risk we can take is to try the same old politics with the same old players and expect a different result. You have shown what history teaches us that at defining moments like this one, the change we need doesn't come from Washington. Change comes to Washington. Change happens because the American people demand it because they rise up and insist on new ideas and new leadership, a new politics for a new time."
In his Democratic nomination acceptance speech, Obama sharply contrasted his candidacy with Arizona Sen. John McCain, mentioning his Republican rival about 21 times.
"John McCain has voted with George Bush ninety percent of the time," Obama said. "Senator McCain likes to talk about judgment, but really, what does it say about your judgment when you think George Bush was right more than ninety percent of the time? I don't know about you, but I'm not ready to take a ten percent chance on change."
Rumors swirled at the convention center that McCain would announce his vice presidential candidate tonight.
However ABC News' George Stephanopoulos reports a senior campaign official said, "There will be no announcement tonight. There will be no leak tonight. This is Barack Obama's night. His nomination is a singular achievement. Tonight's his night to make his case."
Obama aggressively argued that an Obama White House would keep Americans safe. It's a weak spot for Obama, with the latest ABC News/Washington Post poll showed McCain leading Obama by 2-1 margins as more knowledgeable on world affairs and as better-suited to be Commander-in-Chief.
Taking the fight to McCain, Obama aggressively attacked the GOP nominee, and defended Democrats' ability to keep the nation safe.
"John McCain likes to say he'd follow Osama bin Laden to the gates of hell. But he won't even follow him to the caves he lives in," Obama said.
"We are the party of Roosevelt. We are the party of Kennedy. So don't tell me that Democrats won't defend this country," Obama said. "Don't tell me that Democrats won't keep us safe. The Bush-McCain foreign policy has squandered the legacy that generations of Americans -- Democrats and Republicans -- have built, and we are to restore that legacy."
"As Commander-in-Chief, I will never hesitate to defend this nation, but I will only send our troops into harm's way with a clear mission and a sacred commitment to give them the equipment they need in battle and the care and benefits they deserve when they come home," he said.
Obama also pledged to "end this war in Iraq responsibly, and finish the fight against al Qaeda and the Taliban in Afghanistan" -- using softer language than his calls for "immediate" withdrawal of US troops in Iraq at the beginning of his campaign.
Obama ended his speech with a rousing request for people to vote for him in November.