As Obama reminisced on accepting the party's nomination 16 years ago, he spoke about choosing President Joe Biden to be his running mate.

"And looking back, I can say without question that my first big decision as your nominee turned out to be one of my best, and that was asking Joe Biden to serve by my side as vice president," he said.

"Other than some common Irish blood, Joe and I come from different backgrounds," he continued. "When we became brothers, and as we worked together for eight, sometimes pretty tough, years. What I came to admire most about Joe wasn’t just his smarts; his experience. It was his empathy, and his decency. And it’s hard earned resilience. His unshakable belief that everyone in this country deserves a fair shot. And over the last four years, those are the values America has needed most."

Obama went on to praise Biden's leadership as president and for putting the nation before his personal ambition by stepping aside.

"History will remember Joe Biden as an outstanding president who defended democracy at a moment of great danger," Obama said. "And I am proud to call him my president, but I am even prouder to call him my friend."

The former president received a warm welcome from the crowd in the United Center, who revived his iconic campaign slogan "Yes we can!"

"I'm feeling fired up!" Obama said. "I am feeling ready to go -- even If I am the only person stupid enough to speak after Michelle Obama."

Michelle Obama reminds everyone why she’s on of the Democratic Party’s most popular figures. She consistently polls as someone Democrats would like to see run for president -- and this speech showed why.

-ABC News' Tal Axelrod

In her closing remarks, former first lady Michelle Obama warned that a handful of votes in select states would decide the election and pushed Americans to come out to the polls.

"So we need to vote in numbers that erase any doubt we need to overwhelm any effort to suppress us. Our fate is in our hands," she said.