The former president blasted his successor and told his audience in Philadelphia: “Tweeting at the TV doesn’t fix things.”
It is the first time that Mr Obama has been out on the campaign trail in person for his former vice president Joe Biden following a series of online appearances.
And he did not waste any time in taking shots at Mr Trump.
“I get that this president wants full credit for the economy that he inherited, and zero blame for the pandemic that he ignored," said Mr Obama.
“But you know what the job doesn't work that way. Tweeting at the television doesn't fix things. Making stuff up doesn't make people's lives better. You've got to have a plan, you’ve got to put in the work.”
Mr Obama said that he had left the White House a playbook to deal with a pandemic but joked that Mr Trump was probably using it “to prop up a wobbly table somewhere.”
“Donald Trump isn’t suddenly going to protect all of us, he can’t take the basic steps to protect himself,” said Mr Obama. “Just last night he complained that the pandemic made him go to work, he was upset, if he had actually been working the whole time it would never have got this bad.
“Somehow the idea that this White House has done anything but screw this up is just not true.”
Mr Obama then attacked Mr Trump for the economic damage he said his successor had caused the US.
“He did inherit the longest streak of job growth in American history but just like everything else he inherited he messed it up," said Mr Obama.
"The economic damage he inflicted by botching the pandemic response means he will be the first president since Herbert Hoover to actually lose jobs.”
Mr Obama then said that Mr Biden would “restore our standing in the world.”
“A nation that stands with democracy not dictators,” said Mr Obama. “With Joe and Kamala at the helm you are not going to have to think about the crazy things they said every day and that is worth a lot.
"You are not going to have to argue about them every day. It just won’t be so exhausting.
"You may be able to have Thanksgiving dinner without having an argument.
"You'll be able to go about your lives knowing that the president is not going to retweet conspiracy theories about secret cabals running the world or that Navy SEALs didn't actually kill bin Laden.
“Think about that. The president of the United States retweeted that. Imagine. What? What?”
Mr Obama added that the country would not accept the president’s behaviour from anyone but a “crazy uncle.”
The former president then hit out at the “lies” the American people had been told by Mr Trump. "Our democracy is not gonna work if the people who are supposed to be our leaders lie every day and just make things up.
“And we just become numb to it, we just become immune to it. Every single day, fact checkers can’t keep up.”
Mr Obama told the crowd, all of whom were in their cars, that they needed to “reclaim” American principles of “truthfulness and democracy and citizenship.”
And he urged them to turn out and vote because they could not “leave any doubt in this election.”
“We cannot be complacent, I dont care about the polls," said Mr Obama.
He finished his speech by telling supporters that they had to outwork Mr Trump and his supporters.
“We can’t abandon people who are hurting right now," he said.
"We can’t just imagine a better future we have to fight for it, we have to outwork the other side, we have to out-hustle the other side, vote like never before and leave no doubt."
And he added: “America is a good and decent place, but we've just seen so much noise and nonsense that sometimes it's hard for us to remember.
"Philadelphia, I am asking you to remember what this country can be.”