Specifically targeting voters who might be disillusioned, Obama offered a defence of the nation's decency and personal validation that Biden and his running mate, California Senator Kamala Harris, can live up to it.
"America is a good and decent place, but we've just seen so much nonsense and noise that sometimes it's hard to remember," he said.
"I'm asking you to remember what this country can be. ... I'm asking you to believe in Joe's ability and Kamala's ability to lead this country out of these dark times and help us build it back better."
Obama had a number of sharp digs at his successor, saying: "Donald Trump isn't suddenly going to protect all of us. He can't even take the basic steps to protect himself".
He said: "[Trump] hasn't shown any interest in doing the work, or helping anybody but himself and his friends, or treating the presidency, like a reality show that he can use to get attention. And by the way, even then his TV ratings are down. So you know that upsets him.
"But the thing is this is not a reality show. This is reality, and the rest of us have had to live with the consequences of him, proving himself incapable of taking the job seriously," Obama added.
"Philadelphia, I am asking you to remember what this country can be. We can't abandon those who are hurting right now."
He ended with: "Are you fired up? Are you ready to go?"
Obama, 59, said he understood young voters' scepticism and disinterest, recalling his own attitude decades ago. "I'll confess, when I was 20 years old, I wasn't all that woke," he said, adding that young Black men are "not involved because they're young and they're distracted."
But he said not voting gives away power.
"The answer for young people when I talk to them is not that voting makes everything perfect," Obama said. "It's that it makes things better" because politicians respond to and reflect the citizens who cast votes.
"One of the biggest tricks that's perpetrated on the American people is this idea that the government is separate from you," Obama said. "The government's us. Of, by and for the people. It wasn't always for all of us, but the way it's designed, it works based on who's at the table."
- AP