Elizabeth Warren, Kirsten Gillibrand, Kamala Harris, John Delaney and Julian Castro are among those who have also announced their intention to run.
Once dismissed by many as a fringe candidate with wacky socialist ideas, Bernie Sanders campaigned to the brink of the Democratic presidential nomination in 2016 and has now set his sights on the White House once again.
In a statement, Republican National Committee spokesperson Michael Ahrens said of the Independent Vermont senator's bid: "Bernie Sanders is a self-avowed socialist who wants to double your taxes so the government can take over your health care".
While she ultimately became the party's nominee, his campaign helped lay the groundwork for the leftward lurch that has dominated Democratic politics in the Trump era.
An outspoken critic of President Donald Trump, Mr Sanders has described him as a "pathological liar" and "racist".
Among those already in the Democratic race are fellow Senators Cory Booker of New Jersey, Kamala Harris of California, Kirsten Gillibrand of New York, Amy Klobuchar of Minnesota and Elizabeth Warren of MA.
"Together, you and I and our 2016 campaign began the political revolution", Sanders wrote in an early morning email.
Back in the Bronx, Ocasio-Cortez says to keep up the fight
Host Erin Burnett read Ocasio-Cortez's tweet celebrating the decision and asked if she shared her sentiment. Even Trump hating entertainer Cher called out Cortez.
Nigeria's biggest Indian oil buyer signs first deal for USA oil
India is feasting on Venezuelan oil, after the USA imposed a de facto ban on crude imports from the Latin American nation. Bank of America Merrill Lynch said in a note that the Sino-American trade dispute was hurting economic growth globally.
3 kids, 1 woman found fatally shot in MI
The Sheriff's Department is now on scene of the shooting on 19 Mile Road NE near Division Avenue, which is west of Cedar Springs. Four people have been shot and killed in northern Kent County, of which Grand Rapids is the county seat.
Sanders also emphasized the urgency of unseating President Donald Trump, who he called "an embarrassment to our country". Sherrod Brown of OH and former New York City mayor Michael Bloomberg, are also mulling bids for the Democratic nomination.
Over seven pages, the team outlined a strategy for winning black voters that included using social media influencers and having Mr. Sanders give a major speech on discrimination in a city like St. Louis or Cincinnati.
Throughout the 2016 primary, Sanders went from a relative unknown to a political figure known the world over for his support of free healthcare, free college tuition and other social-democratic policies. Sanders identifies as an Independent though in 2016 he sought the nomination from the Democratic party, an received less than fulsome support from the Democratic party.
Sanders has been an unsparing critic of Trump, and in his email he called him "the most risky president in modern American history".
Sanders used his announcement to attack President Donald Trump, saying: 'We are living in a pivotal and unsafe moment in American history. Mr. Sanders's inner circle did not respond.
Before his election to the Senate in 2006, Sanders represented Vermont's at-large congressional district in the House for 16 years.
At one point during the interview, Kinzel asked Sanders whether he represents "the face of the new Democratic Party".