The US Libertarian party has nominated Chase Oliver as its presidential candidate after members rejected overtures from Donald Trump and Robert F Kennedy Jr.

Oliver, 38, who describes himself as “armed and gay”, was chosen at the party’s convention in Washington DC on Sunday at the end of seven rounds of voting that lasted seven hours.

Accepting the nomination, he vowed to be “the only national candidate” – contrasting himself to Trump, Kennedy and President Joe Biden – in the presidential poll and called for a ceasefire in Israel’s war with Hamas in Gaza, saying “end the genocide”.

Oliver’s victory followed separate pitches to the Libertarian convention – staged against the backdrop slogan of “Become Ungovernable” – by Trump and Kennedy for the backing of a party that could win a significant enough proportion of the popular vote to swing what is expected to be a close election.

Trump has been running narrowly ahead of Biden in most nationwide polls, while Kennedy – with the advantage of name recognition through being a member of America’s most storied political family dynasty – has been consistently running at around or above 10%, making him a potential spoiler candidate.

With the party platform dedicated to individual freedom and small government, members booed and jeered Trump on Saturday when he addressed them in a bid to win their support.

“We should not be fighting each other,” Trump – the former president and presumed Republican nominee – told the gathering, only to be greeted with a chorus of profane catcalls. “Combine with us in a partnership – we’re asking that of the libertarians. We must work together. Combine with us. You have to combine with us.”

Kennedy, the son of the former attorney general Robert F Kennedy and running as an independent after initially trying to win the Democratic nomination, earned a warmer reception after pledging to pardon Edward Snowden, the National Security Agency whistleblower now exiled in Russia, and drop espionage charges against Julian Assange.

But he was eliminated in the first round of Sunday’s voting after winning just 19 votes, 2% of the total. Trump, who was not an official potential nominee, won six write-in votes.

In his acceptance speech, Oliver took aim at both candidates, as well as Biden.

“Rule No 1: If you want to elect a real political outsider, don’t elect somebody with the last name Kennedy,” he said.

Referring to the advanced years of Trump and Biden, aged 77 and 81 respectively, he said younger voters “don’t want octogenarians running their lives”.

The party, which expects to be on the ballot in at least 37 states, won 1.2% of the popular vote in the 2020 election.

• US elections 2024
• US politics
• Donald Trump
• Joe Biden
• Robert F Kennedy Jr
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