Robert F Kennedy Jr to challenge Biden for White House
The 69-year-old is the son of assassinated Senator Robert F Kennedy and nephew of President John F Kennedy.
The environmental lawyer's campaign treasurer, John E Sullivan, confirmed the filing on Wednesday.
Mr Kennedy is an outspoken anti-vaccine campaigner. Instagram removed his account in 2021 for "repeatedly sharing debunked claims", the company said.
US President Joe Biden has indicated he will run for re-election, though he has not yet formally declared his candidacy.
He was previously expected to launch his campaign in early April, but top aides say his timeline has shifted.
CBS News, the BBC's US partner, has reported that he is expected to formally announce a run in early summer now.
Last month, another Democrat, Marianne Williamson, jumped into the presidential race.
In March, Mr Kennedy shared on Twitter that he was considering a run for president.
At the time, he said: "If I run, my top priority will be to end the corrupt merger between state and corporate power that has ruined our economy, shattered the middle class, polluted our landscapes and waters, poisoned our children, , and robbed us of our values and freedoms."
As the co-founder of an environmental law firm, Mr Kennedy won plaudits for campaigning on issues such as clean water, including working to clean up the Hudson River in New York.
But his anti-vaccine views have provoked a strong backlash, including from his own family. In 2021 his sister, Kerry Kennedy, called him "very dangerous" on the issue.
In 2019, three other family members penned an op-ed in the news outlet Politico, denouncing Mr Kennedy's anti-vaccine views.
His sister Kathleen Kennedy Townsend, brother Joseph P Kennedy II and niece Maeve Kennedy McKean said his views were "tragically wrong" and have "deadly consequences".
In 2022, Facebook and Instagram removed accounts for an anti-vaccine group founded by Mr Kennedy, Children's Health Defense, for "repeatedly" violating company policies on medical misinformation.
During the coronavirus pandemic, the organisation flourished, its revenue doubling to $6.8m (£5.5m).
Mr Kennedy had also published a book, The Real Anthony Fauci, in which he accused the former US infectious disease chief of "a historic coup d'etat against Western democracy".
Mr Kennedy also invoked Nazi Germany during an anti-vaccine speech in Washington, DC last year.
He has also invoked imagery of John F Kennedy in his anti-vaccine work.
Mr Kennedy has a voice disorder, spasmodic dysphonia, which affects the muscles in the voice box.
He married actress Cheryl Hines in 2014 and lives Los Angeles, California.