"Kamala emphatically shows us that she is the one president this country needs right now," said Obama.
"If this election goes the wrong way, this backward vision of America being spewed by Kamala's opponent, it will affect all of our lives. No matter how old we are," she added.
That's when the crowd started chanting, "We're not going back."
Obama, along with artist Alicia Keys, said a vote for Harris means a better future for all.
"We believe every life has equal value. We want peace in our world and a healthy planet and a just society, and Kamala and Tim Walz assure me that this is what she believes and will work hard to fulfill," said Keys.
Meanwhile, former President Donald Trump's team continued their bus tour across Pennsylvania.
Among the stops was Ludwig's Construction Equipment in Glenmoore before they headed to locations in Broomall and Lansdale.
A number of Republican congressmen, including Byron Donalds, Ronny Jackson, and Mark Green along with other Trump supporters encouraged people to get out the vote.
"Are you ready to drag people to the polls, kicking and screaming?'" said Jeff Bartos. "Are you ready to elect Donald J. Trump as the 47th president of the United States?"
Trump's son, Eric, also rallied supporters at an appearance near Pittsburgh.
"Early vote numbers have been great. People must get out," said Eric. "Obviously, Pennsylvania is going to be razor thin. It always is, I think there is a lot of enthusiasm out there."
"It actually may be the only thing Kamala Harris and Donald Trump agree on - whoever wins Pennsylvania is likely to be the next president of the United States," said Governor Josh Shapiro.
Trump has a rally in Lancaster County on Sunday.
On Monday, both candidates have several events across Pennsylvania, andHarris will end the day in Philadelphia for a rally and concert on the Benjamin Franklin Parkway.