But Obama argued, "Kamala Harris won't be focused on her problems – she'll be focused on yours."
"Kamala Harris is ready for the job. This is a person who has spent her life fighting on behalf of people who need a voice and a champion," Obama said.
The former president said that Harris, while working as a prosecutor in California, "stood up for children who had been victims of sexual abuse."
"As Attorney General of the most populous state in the country, she fought big banks and for-profit colleges, securing billions of dollars for the people they had scammed," he said. "After the home mortgage crisis, she pushed me and my administration hard to make sure homeowners got a fair settlement."
Obama also praised Harris' running mate, Minnesota Gov. Tim Walz.
"I love this guy," Obama said, before cracking: "You can tell those flannel shirts he wears don't come from some consultant, they come from his closet, and they've been through some stuff."
Obama also had warm words for President , who served as his vice president for two terms, and who last month dropped out of the election contest and endorsed Harris to replace him on top of the Democratic ticket.
"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," Obama said.
"Other than some common Irish blood, Joe and I come from different backgrounds," he said. "But we became brothers. And as we worked together for eight years, what I came to admire most about Joe wasn't just his smarts and experience, but his empathy and his decency; his hard-earned resiliency and his unshakable belief that everyone in this country deserves a fair shot."
