The 76-year-old, who has already run twice for the presidency, enters a crowded race for the 2020 Democratic nomination. He is up against 19 other hopefuls.
In a video posted on Twitter, Biden focused on the 2017 deadly clash between white supremacists and counter protesters in Charlottesville, Virginia. Biden noted US President Donald Trump’s comments that there were some “very fine people” on both sides of the violent encounter, which left one woman dead.
“We are in the battle for the soul of this nation,” Biden said. “If we give Donald Trump eight years in the White House, he will forever and fundamentally alter the character of this nation – who we are. And I cannot stand by and watch that happen.”
The announcement follows months of speculation over whether Biden, a Democratic party stalwart and an early leader in opinion polls, would launch a bid for his party’s nomination to challenge Trump in 2020.
Biden served eight years as vice president under President Barack Obamaand 36 years in the US Senate. At 76, he is the second oldest candidate in the Democratic nominating contests, after 77-year-old Senator Bernie Sanders.
What reaction has there been?
A spokesman for Mr Obama said selecting Mr Biden as his running mate “was one of the best decisions he ever made” and the two had “forged a special bond”, but the former president notably stopped short of an endorsement.
A source familiar with Mr Obama’s thinking said the former president believed “a robust primary in 2007 and 2008 not only made him a better general election candidate, but a better president, too”.