Donald Trump is nominating Oklahoma senator Markwayne Mullin to lead the Department of Homeland Security, handing control of the administration’s sweeping immigration and deportation agenda to one of Washington’s most hardline voices and combative allies on the issue.

The announcement came Thursday as Trump ousted Kristi Noem following a catastrophic week on Capitol Hill, in which Republican lawmakers grilled her over a $220m advertising contract that prominently featured her own image. The White House had publicly denied Trump ever approved the campaign.

The first-term Mullin, 48, spent a decade in the House before winning a special election for his Oklahoma Senate seat in 2022, with Donald Trump’s endorsement. A member of the Cherokee nation, he studied construction technology rather than completing a four-year degree, and is widely reported to be the only sitting senator without a bachelor’s degree.

His record on immigration enforcement has aligned closely with Trump’s hardline stance. He co-sponsored the Laken Riley Act, which mandates ICE detention for undocumented immigrants charged with theft or burglary until deportation proceedings are complete. He has long defended ICE, criticized sanctuary city policies as an obstruction of federal law, and consistently frames mass deportation as a legal obligation.

Throughout Trump’s second term, he has become one of the most visible Republican voices on social media and on the Sunday shows, a reliable and combative surrogate for an administration that prizes both qualities.

When Democrats sought some reforms to immigration enforcement practices during a standoff over DHS funding earlier this year, Mullin dismissed their position in an appearance on CNN’s State of the Union. “They’re not stopping ICE from doing their job. They’re not stopping the Border Patrol from doing their job. All this is political theater,” he said.

The homeland security department has been partially shut down since 14 February, after Senate Democrats blocked a funding bill in the wake of the killing of Renee Nicole Good and Alex Pretti by federal immigration agents in Minnesota.

In January, as criticism of the agency mounted following Pretti and Good’s deaths, Mullin went on social media to say that he stands with DHS, and that “ICE agents aren’t Disney villains”.

“These Immigration and Customs Enforcement officers are red-blooded American patriots doing a tough job to keep our nation safe,” he wrote.

Perhaps his most striking remarks came last year on NBC’s Meet the Press, when host Kristen Welker asked what should happen to babies born on US soil, currently protected under the 14th amendment, whose undocumented parents are deported. Mullin said “they should go where their parents are”, describing a situation where American-born infants would be deported too.

“Why wouldn’t you send a child with their parents?” he said. “Why would you want to separate them?”

Mullin’s record away from the Senate floor has also drawn scrutiny. In a video posted to X last year, he recounted the 1890 story of a newspaper columnist who shot dead a former congressman with whom he had been feuding, suggesting that journalists might write fewer “fake news” stories if politicians could still “handle our differences that way”. He later insisted he had been joking.

Before politics, Mullin built a family plumbing business in Westville, Oklahoma into a multi-state company worth millions of dollars. He is also, according to Tapology, a retired professional fighter with a perfect 3-0 record, last competing in April 2007 at 5ft 8in from Westville, Oklahoma.

He told RollCall in 2014 that he is the youngest of seven children in his family, and that his compound name is a mashup of the first names of two uncles.

Trump said Mullin “will become the United States Secretary of Homeland Security, effective March 31, 2026”.

Mullin would be allowed to serve as acting secretary as long as his nomination is formally pending, but cabinet secretaries require Senate confirmation, involving committee hearings, financial disclosures, a background check, and a floor vote. With less than a month until the self-imposed start date, that timeline could be difficult to meet.

When naming him to succeed Noem, Trump called Mullin a “Maga warrior” and highlighted his undefeated MMA career.

“Markwayne truly gets along well with people and knows the wisdom and courage required to advance our America First agenda,” Trump wrote. “As the only Native American in the Senate, Markwayne is a fantastic advocate for our incredible tribal communities.”