Robert F. Kennedy Jr. has dropped out of the race for the White House and endorsed Donald Trump for US president.
The independent candidate joined Trump on a stage in Arizona on Friday night and said that he had decided "to throw my support to President Trump".
Kennedy, whose support was at 8.7 per cent in a nationwide poll by The Hill this week, gives the Trump campaign a major boost in what has become a close race.
Analysts say that in the tight race between the Democratic Party's Kamala Harris and Trump for the presidency, the votes of Kennedy's supporters could determine the outcome in some battleground states.
Kennedy, the scion of America's most famous political clan, is an environmental lawyer and long-time vaccine skeptic whose campaign struggled to gain traction with mainstream voters.
Members of his family issued a public statement to distance themselves from his endorsement and said they were backing the Democrat Harris-Walz ticket.
He said he had launched his campaign in April 2023 "as a Democrat, the party of my father, my uncle... the champions of the Constitution".
But he left because "it had become the party of war, censorship, corruption, big pharma, big tech, big money".
He told reporters that Trump's insistence he could end the war in Ukraine by negotiating with Russia "alone would justify my support for his campaign".
"There are still many issues and approaches on which we continue to have very serious differences. But we are aligned on other key issues."
Kennedy has now moved to have his name removed from the ballot in 10 states, having already withdrawn from the race in Arizona and Pennsylvania.
It is too late for his name to be removed from some swing states, such as Nevada and Wisconsin, election officials told AP news agency.
His withdrawal confirms a report in The New York Times on Wednesday which, citing three anonymous sources, said Kennedy would end his campaign and potentially endorse Trump. CNN also cited two anonymous sources who reported Kennedy was expected to suspend his campaign on Friday.
Trump said earlier this week he would "certainly" be open to Kennedy playing a role in his administration if he was elected.
"He's a brilliant guy. He’s a very smart guy," Trump told CNN. "I've known him for a very long time.
"I didn't know he was thinking about getting out, but if he is thinking about getting out, certainly I'd be open to it."
Known for sometimes bizarre pronouncements and for spreading often dangerous health-related conspiracy theories, Kennedy has faced a number of setbacks in his electoral campaign.
This month, a judge in New York claimed that Kennedy had falsely claimed residency in the state and barred him from ballots there.