President-elect Trump’s chief speechwriter, Stephen Miller, will serve as senior adviser for policy in the next administration, transition officials announced Tuesday.

Miller has been a part of the incoming Republican president’s close circle of advisers since January. He assisted Trump with major speeches on myriad policy issues during the campaign and has overseen policy development efforts on the transition operation since the president-elect’s victory last month. When Trump enters office on Jan. 20, Miller will be in charge of all White House policy staffers and responsible for pushing the president-elect’s policy agenda.