President Donald Trump has named Stephen Miller, the architect of his hardline immigration policy, as his new chief of staff following historic losses in the US midterm elections.

Miller replaces Susie Wiles, who submitted her resignation after Republicans lost control of both chambers of Congress, delivering a blow to the prospects for Trump’s agenda in his final two years in the White House.

Trump said Wiles did an “outstanding job” and would be moved to the “Trump Political Operation”.

Miller, a Trump loyalist and deputy chief of staff who served as a senior adviser during his first administration, is set to take on the new role on Monday.

One of Trump’s closest aides, Miller stuck by the president following his 2020 election defeat, and followed Trump back into power last year.

Wiles gave her resignation to Trump on Thursday night, a US official told CBS News, the BBC’s media partner. Three sources told CBS she quit because of the election losses.

In a statement, she said being on Trump’s team was “the honor of a lifetime”.

“I’m so proud to have been a part of what we’ve accomplished together from securing our border and cutting taxes to strengthening our economy and putting America First,” she said. “While my role may be changing, my commitment to the President and the mission never will.”

It was unclear if her deputies would remain at the White House.

Wiles, 69, is seen as among the most powerful figures in the Trump administration and someone particularly close to the US president.

Asked last month whether Wiles could be replaced soon, Trump said there was “zero chance”.

“Susie is here and she’s gonna be here for a long time,” he said.

Wiles recently battled cancer, announcing in September, six months after her diagnosis, that she was in remission.

Wiles is not the only high-profile Trump official to leave this week following the midterm elections, which have prompted a reckoning among Republicans about how to address voters’ rebuke of Trump’s agenda.

Several justice department officials have also resigned, including John Eisenberg, the head of the department’s National Security Division, and Jason Reding Quiñones, who was known for enforcing conspiracy probes into officials investigating Trump’s handling of classified documents.

Democrats took to social media to criticise Trump’s new pick, accusing him of doubling down despite voters’ anger with his party’s agenda.

Democratic Congressman Robert Garcia, who would lead the House Oversight Committee after Democrats take control of the chamber, said he would continue to investigate Miller and his “misconduct”.

“Just days after the American people rejected his corrupt and lawless presidency, Donald Trump is doubling down. Stephen Miller is the architect of the unconstitutional ICE raids that have terrorized our communities and kidnapped and killed American citizens and immigrant families,” he said, referencing US Immigration and Customs Enforcement.

Trump’s communications director Steven Cheung called Miller “someone who has been with the President since the very beginning”.

“There is no bigger advocate for the Trump agenda than Stephen, and he will help the Administration deliver on monumental victories for the rest of this historic second term,” he said.