Ms. Hicks, 29, a former model who joined Mr. Trump’s 2016 presidential campaign without any experience in politics, became known as one of the few aides who understood his personality and style and could challenge the president to change his views.
Ms. Hicks had been considering leaving for several months. She told colleagues that she had accomplished what she felt she could with a job that made her one of the most powerful people in Washington, and that there would never be a perfect moment to leave, according to White House aides.
The announcement comes just one day after Hicks testified for several hours before the House Intelligent Committee.
President Donald Trump responded to the news with praise for Hicks:
“Hope is outstanding and has done great work for the last three years,” Mr. Trump said. “She is as smart and thoughtful as they come, a truly great person. I will miss having her by my side, but when she approached me about pursuing other opportunities, I totally understood. I am sure we will work together again in the future.”