Harris also tweeted: "Joe Biden can unify the American people because he's spent his life fighting for us. And as president, he'll build an America that lives up to our ideals. I'm honoured to join him as our party's nominee for Vice President, and do what it takes to make him our Commander-in-Chief.”
She is the fourth woman on a major presidential ticket, after Democratic vice presidential nominee Geraldine Ferraro in 1984, Republican vice presidential nominee Sarah Palin in 2008 and Democratic presidential nominee Hillary Clinton in 2016.
Biden's announcement was a long time in the making. During a debate on March 15, the Presidential hopeful committed to selecting a woman as his running mate.
"I commit that I will, in fact, appoint a woman to be vice president," he told CNN."There are a number of women qualified to be president tomorrow." He reiterated that promise in a tweet that same night.
The historical announcement has stirred together a lot of thoughts from Twitter.
Katie Holmes' post in support of Biden and Harris' pairing got considerable traction, captioning: "#BidenHarris2020." Celebrity friends, including Zoe Kravitz, quickly approved.
Here's how the world is reacting to the news: