The Senator, who has served Vermont since 2007, lost the Democratic Party leadership to Hillary Clinton in the 2016 White House campaign. But the progressive populist is hoping for a second chance to share his policies of expanding health care and making higher education free.
He announced his plans to run for president in an email to his one million supporters this morning.
He wrote: “Our campaign is about creating a government and economy that works for the many, not just the few.
“Together, you and I and our 2016 campaign began the political revolution. Now, it is time to complete that revolution and implement the vision that we fought for.”
Some of his contenders 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 Massachusetts.
If picked to represent the Democrats in the presidential race, Mr Sanders will likely face current President Donald Trump, who is a Republican, in the next general election.
He has been a huge critic of Mr Trump since he was elected in 2016.
In his email, Mr Sanders called him “the most dangerous president in modern American history”.
He said: “We are running against a president who is a pathological liar, a fraud, a racist, a sexist, a xenophobe and someone who is undermining American democracy as he leads us in an authoritarian direction.”
How old will Bernie Sanders be if he becomes US president in 2020?
Mr Sanders was born on September 8, 1941, which makes him 77-years-old.
If he wins the presidential election on Tuesday, November 3, 2020, he will be 79.
Donald Trump currently has the record of being the oldest president, as he was 70-years-old at his inauguration.
Mr Sanders is a former mayor of Burlington, Vermont, and won a US House of Representatives seat in 1990.
This made him the first independent elected to the House in 40 years.
In 2006, he won a US Senate seat and in 2018 was voted in for a third six-year term.
But as he will be almost 80 at the next presidential election, he is also likely to face questions about his age and relevance in a party that is increasingly advancing more diverse and fresh voices.
This include women and minorities – groups he struggled to win over in 2016.