Harris, 55, was long considered the front-runner for the job. She is already known nationally and was tested on the campaign trail and in the media during her own presidential bid last year.
Biden called her “a fearless fighter for the little guy, and one of the country’s finest public servants” in a tweet Tuesday.
She also seemed to be an obvious fit for three key criteria that Biden publicly laid out for his running mate ― accomplished enough to be “ready to be president,” a similar mindset on key issues, and a woman.
Biden and Harris are scheduled to deliver their first public remarks together Wednesday in Delaware.
President Barack Obama praised the announcement, saying, “Joe Biden nailed this decision.”
“I’ve known Senator Harris for a long time,” Obama said in a statement. “She is more than prepared for the job. … Her own life story is one that I and so many others can see ourselves in: a story that says that no matter where you come from, what you look like, how you worship, or who you love, there’s a place for you here. It’s a fundamentally American perspective, one that’s led us out of the hardest times before. And it’s a perspective we can all rally behind right now.”