Biden also unveiled his campaign website. Check it out here.
Here are the latest updates:
Update 1:24 p.m. EDT April 25: Biden has announced his senior campaign staff, NBC News reported.
Greg Schultz will be his campaign manager with Kate Bedingfield serving as his deputy campaign manager and communications director.
Update 1:03: p.m. EDT April 25: Biden said he did not ask for an endorsement from former President Barack Obama.
"I asked President Obama not to endorse," The Associated Press reported Biden saying. "Whoever wins this nomination should win it on their own merits."
After the announcement, Biden appeared in his home town of Wilmington, Delaware, WPVI reported.
He stopped at a Wilmington restaurant and spoke to customers as he waited for his to go meal, The Washington Post reported.
A reporter then asked him what his message to the world was, with Biden responding, "America's coming back like we used to be -- ethical, straight, telling the truth ... supporting our allies, all good things," the Post reported.
Update 8:24 a.m. EDT April 25: President Donald Trump responded to Biden's announcement in a tweet Thursday morning.
"Welcome to the race Sleepy Joe," Trump tweeted. "I only hope you have the intelligence, long in doubt, to wage a successful primary campaign. It will be nasty – you will be dealing with people who truly have some very sick & demented ideas. But if you make it, I will see you at the Starting Gate!"
Update 7:07 a.m. EDT April 25: Former President Barack Obama's spokeswoman released a statement early Thursday following Biden's announcement.
"President Obama has long said that selecting Joe Biden as his running mate in 2008 was one of the best decisions he ever made," Obama spokeswoman Katie Hill said. "He relied on the Vice President's knowledge, insight and judgment throughout both campaigns and the entire presidency. The two forged a special bond over the last 10 years and remain close today."
Meanwhile, U.S. Sen. Chris Coons, D-Del., endorsed Biden in a statement.
"We are at a crucial moment in our history," Coons' statement read. "We need leaders who will bring us together instead of tearing us apart, who will focus on the real issues facing American families, and who will restore the United States' role in the world as a force for stability, freedom and human rights. Joe Biden is that leader, and I'm proud to endorse him for President of the United States."
U.S. Sen. Bob Casey, D-Pa., also endorsed Biden.
"At this make-or-break moment for our middle class, our children and our workers, America needs Vice President Joe Biden to be its next President," the statement read. "Joe Biden has spent a lifetime fighting battles on behalf of hardworking Americans while ensuring America's values and interests are represented abroad. As both a U.S. Senator and our Vice President, he has delivered results for the middle class, kept our country safe and strengthened our standing in the world."
Original story: A fundraiser for Biden, who is originally from Scranton, Pennsylvania, also is scheduled Thursday evening in Philadelphia, Politico reported Tuesday.
On Monday, Biden, 76, will make an appearance at a Pittsburgh union hall for his first campaign event, NBC News reported.
Biden, who served in the U.S. Senate from 1973 to 2009, unsuccessfully sought the Democratic nomination for president in 1988 and 2008. This time, he joins a packed field of 20 Democratic candidates vying to take on Republican President Donald Trump.
Biden consistently has performed well in recent polls. In a national survey of Democrats released by Monmouth University this week, Biden led the field with 27% support, The Hill reported. He's also leading the Democratic pack in the RealClearPolitics polling average, with 29% support.
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But the Monmouth poll found that Biden's favorability rating dropped from 76% in March to to 72% this month, according to The Hill. The drop came as multiple women came forward to accuse him of inappropriate contact.
"I will be more mindful and respectful of people's personal space, and that's a good thing, that's a good thing," he said earlier this month. "I've worked my whole life to empower women. I've worked my whole life to prevent abuse, I've written, and so the idea that I can't adjust to the fact that personal space is important – more important than it's ever been – is just not thinkable. I will. I will."