Nikki Haley ended her presidential campaign on Wednesday after being soundly defeated in coast-to-coast Super Tuesday contests, in effect ceding the 2024 Republican nomination to Donald Trump.

The former South Carolina governor, who became Trump’s UN ambassador and the first prominent woman of color to seek the Republican nomination for president, declined to immediately endorse the former president as nearly all of his other Republican rivals did. Instead she challenged Trump to earn the support of her voters, calling it his “time for choosing”.

“The time has now come to suspend my campaign,” Haley said, announcing her decision during a three-minute speech in Charleston, South Carolina. “It is now up to Donald Trump to earn the votes of those in our party and beyond who did not support him and I hope he does that.”

After vanquishing Haley in 14 out of 15 Republican primary elections, Trump is on the verge of securing enough delegates to clinch his party’s nomination for a third consecutive time despite facing 91 criminal charges, attempts to remove him from the ballot for inciting an insurrection and civil court rulings requiring him to pay more than $400m having been found liable for financial fraud and defamation. Joe Biden, meanwhile, swept past his nominal challengers on his inexorable march to the Democratic nomination. Haley’s departure from the race in effect ends the primary season, far earlier than in past cycles, setting the stage for a Trump-Biden rematch she tried to forestall.

Haley had previously pledged to the Republican National Committee that she would support the eventual nominee. But Haley recently said she no longer felt bound by the commitment after Trump’s campaign moved aggressively to assume control over the organization despite her continued presence in the race.

In the final weeks of her campaign, Haley had become the leader of her party’s disparate anti-Trump movement. Moving past her initial reluctance to take on Trump, Haley leveled increasingly pointed and personal attacks at her former boss, casting doubt on his mental fitness and loyalty to the US constitution.

Haley had vowed to stay in the race until at least Super Tuesday and for as long as she remained “competitive”. But Tuesday’s results left no path forward for the Republican.

“I said I wanted Americans to have their voices heard. I have done that,” she said on Wednesday. “I have no regrets.”

Among Trump’s prominent primary rivals, Haley was the last candidate left standing, so her withdrawal ensures that Trump will capture the Republican nomination.

Despite enduring a long string of losses, exit polls showed her strength among suburban women and independents – key constituencies in a general election that she warned Trump was continuing to alienate. A sizable share of her supporters – and Republican voters more broadly – say they would not vote for a candidate convicted of a crime.

“At its best politics is about bringing people into your cause, not turning them away,” Haley said in her Charleston speech, “and our conservative cause badly needs more people.”

Ahead of Haley’s remarks on Wednesday, Trump attacked her in a social media post, accusing his rival of drawing support from “Radical Left Democrats” and downplaying her sole win in Vermont. “At this point, I hope she stays in the ‘race’ and fights it out until the end!” he wrote, before inviting her supporters to “join the greatest movement in the history of our Nation”.

Biden by contrast praised the “courage” he said Haley displayed in seeking the Republican nomination despite knowing it was likely to provoke the wrath of Trump and his most loyal supporters.

“Nikki Haley was willing to speak the truth about Trump: about the chaos that always follows him, about his inability to see right from wrong, about his cowering before Vladimir Putin,” Biden said in a statement issued by his campaign. In an appeal to Haley’s supporters, Biden said: “There is a place for them in my campaign.

“I know there is a lot we won’t agree on,” he continued. “But on the fundamental issues of preserving American democracy, on standing up for the rule of law, on treating each other with decency and dignity and respect, on preserving Nato and standing up to America’s adversaries, I hope and believe we can find common ground.”

When Haley launched her campaign just over a year ago, she began as an underdog, polling far behind Trump and his other rivals, including the Florida governor, Ron DeSantis. But she eventually outlasted them all, securing the one-on-one race with Trump that she sought.

She could not quite squeeze DeSantis out of second place in Iowa – both a long way behind Trump, the winner – but she did see him leave the race before the New Hampshire primary. She notched her best performance in the New Hampshire primary, but she still fell 11 points short of Trump in the state, which inspired a rush of fundraising that defied her narrowing path to the nomination.

Ultimately, though, Haley simply could not convince enough Republicans it was time to dump Trump.

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In the Nevada presidential primary, which Trump opted out of, Haley suffered an embarrassing defeat to the ballot line “None of these candidates” and then faced defeat by 20 percentage points in South Carolina, the state that twice elected her governor.

On Tuesday, when voters in 15 states cast ballots in contests known as Super Tuesday, Haley lost every state apart from Vermont. The surprise victory also made history: Haley became the first Republican woman to prevail in a state presidential primary. She had previously only won in Washington DC.

Haley was governor of South Carolina from 2012 to 2017, before resigning in the aftermath of Trump’s shock win in the 2016 presidential election, in order to be appointed US ambassador to the UN. Despite her popularity in South Carolina when she was governor, Haley was unable to carry her home state, sealing her fate in the Republican primary.

In a surprise move, Haley resigned her role as US ambassador to the UN in 2018, becoming one of the few administration officials to leave on relatively good terms with then president Trump. Widely thought to have ambitions to run for president after Trump departed the scene, she denied speculation linking her to a place on his ticket.

Trump did not leave the scene – even after inciting the deadly attack on Congress on 6 January 2021, in an attempt to overturn his defeat by Joe Biden.

When the 2024 race kicked off in earnest, Haley sought to position herself as a fresh alternative to Trump. She made steady inroads in polling, benefiting particularly from strong debate performances while Trump refused to take the stage.

The 51-year-old made electability a centerpiece of her message, arguing she was the only Republican who could beat Biden in a general election. On the campaign trail, she liked to remind voters: “Republicans have lost the last seven out of eight popular votes for president – that’s nothing to be proud of.”

Once elected the “Tea Party” governor, Haley ran as a conservative, seeking to appeal to the base by railing against the size of the national debt and the participation of transgender athletes in women’s sports.

Allies argued that her support for Ukraine in its war with Russia and her relatively nuanced stance on abortion – she called for a “consensus” rather than backing a proposal to ban the procedure after a specific number of weeks – would help the party appeal to independents and suburban women alienated by Trump.

Haley also emphasized her relative youth, asking Republicans to put their faith in a “new generation” of leaders. She made a splash with a call for “mental competency tests” for politicians over 75, a group pointedly including Biden and Trump.