Joe Biden has chosen Kamala Harris, the prominent senator from California whose political career has included many barrier-breaking moments, as his running mate, his campaign announced on Tuesday.

The decision comes more than a year after Harris, who was also a 2020 Democratic candidate, clashed with Biden over racial issues during the first primary debate. If elected, she would be the nation’s first female, first Black and first Asian American vice president.

Picking Harris, who is 55, provides the ticket with some generational diversity. Biden, 77, would be the oldest president-elect in U.S. history.

The announcement from Biden — which a campaign aide told NBC News came about 90 minutes after he called Harris to tell her — caps weeks of speculation and is Biden’s biggest decision to date as the presumptive Democratic nominee, a detail Biden himself noted in his announcement.

"You make a lot of important decisions as president. But the first one is who you select to be your Vice President. I’ve decided that Kamala Harris is the best person to help me take this fight to Donald Trump and Mike Pence and then to lead this nation starting in January 2021," Biden wrote in an email from his campaign to supporters.

"I need someone working alongside me who is smart, tough, and ready to lead. Kamala is that person," he wrote. "I need someone who understands the pain that so many people in our nation are suffering. Whether they’ve lost their job, their business, a loved one to this virus."

"This president says he 'doesn’t want to be distracted by it.' He doesn’t understand that taking care of the people of this nation — all the people — isn’t a distraction — it’s the job," Biden continued. "Kamala understands that. I need someone who understands that we are in a battle for the soul of this nation. And that if we’re going to get through these crises — we need to come together and unite for a better America. Kamala gets that."