Anti-vaccine activist Kennedy, a member of a storied US political dynasty, posted a video on YouTube on Friday asking Americans to join him for a "major announcement" in Philadelphia on October 9.
"I'll be speaking about a sea change in American politics," he said, decrying corruption in "both parties."
"How are we going to win against the established Washington interests?" he asks.
"It's not through playing the game" by the current rules, he said.
Kennedy is nephew of former president John F. Kennedy, who was assassinated in 1963, and the son of Senator Robert F. Kennedy, who was assassinated in 1968 during his own presidential bid.
Kennedy said in April he would challenge Biden for the Democratic nomination to run against the Republican nominee, expected to be former President Donald Trump.
Since then, Kennedy has complained that the Democratic Party has "essentially merged into one unit" with the Biden campaign, denying him a fair shot in the nominating contest. Several opinion polls put Biden way ahead of Kennedy in single digit percentages or low double digits.
Kennedy's plan to run as an independent instead was first reported by Mediaite, a politics website.
Democrats have expressed concern that any third-party bid could draw votes away from Biden, 80, who faces concerns about the economy and his age in an expected rematch against the Republican frontrunner and presumed nominee Trump, 77.
However, Republicans like Kennedy more than Democrats do by a wide margin, opinion polling compiled by FiveThirtyEight showed, suggesting Trump's campaign could be impacted as well. Trump faces four criminal prosecutions, including charges he illegally tried to overturn Biden's 2020 election victory, and his campaign is bleeding cash for legal expenses.
