President-elect Donald Trump is expected to announce that Stephen Miller, an immigration hard-liner and one of his senior advisers, will become his deputy chief of staff for policy, multiple sources familiar with the matter told ABC News.
It's not clear when Trump plans to formally announce the job, the sources said.
Miller worked in the first Trump administration and played a key role in crafting immigration policies -- including those that resulted in thousands of families being separated at the border.
MORE: Trump says former ICE Director Tom Homan will be 'border czar'ABC News reported earlier this week that Miller is expected to drive immigration policy and has already been laying the groundwork on this for months.
Vice President-elect JD Vance posted on X saying, "This is another fantastic pick by the president."
News of Miller's selection comes as Trump's new administration begins to take shape. Last week, he announced his campaign manager, Susie Wiles, would be his White House chief of staff; on Sunday evening, Trump shared that former Immigration and Customs Enforcement Director Tom Homan is going to be the "border czar" in his administration.
Trump also selected Rep. Elise Stefanik to be his U.S. ambassador to the United Nations, sources told ABC News.
MORE: Trump wants a mass deportation program. How much could it cost?After leaving the Trump administration in 2021, Miller became the head of America First Legal, which described itself as the conservative answer to the American Civil Liberties Union.
America First Legal took the Biden administration to court several times over immigration policy, notching a win recently when a federal judge struck down a program known as "Keeping Families Together" that would have provided temporary relief from deportation for undocumented spouses and stepchildren of U.S. citizens by allowing them to apply for legal status without having to leave the country.
America First Legal was also among many groups listed as part of Project 2025, a blue-print for a Republican presidency that generated controversy on the campaign trail and became a target of Democratic criticism. Trump distanced himself from Project 2025 and America First Legal sought to be removed from the website's list of advisory board members.
Miller told ABC News at the time, "I have zero involvement with Project 2025. Zero. None. I made an advice video a long while back for students. I have no involvement with the project whatsoever."
Miller spoke at Trump's Madison Square Garden rally in the final stretch of the race, where he doubled down on Trump's immigration agenda.
"Who is going to stand up and say the cartels are gone, the criminal migrants are gone, the gangs are gone," Miller said. "America is for Americans and Americans only."
The position Miller is set to take on is not a Cabinet position, so it does not need Senate confirmation.
ABC News' Alexandra Hutzler contributed to this report.