The 29-year-old has been a close confidante to the commander in chief for the last three years.
"There are no words to adequately express my gratitude to President Trump," Hicks said in a statement to CBS News. "I wish the president and his administration the very best as he continues to lead our country."
In a statement of his own, Trump said: "Hope is outstanding and has done great work for the last three years. She is as smart and thoughtful as they come, a truly great person."
News of her resignation was first reported by The New York Times.
The announcement came just a day after she was grilled on Capitol Hill for nine hours by the House Intelligence Committee, which is investigating Russia’s involvement in the 2016 election.
Hicks was reportedly cagey with investigators, refusing to answer questions about her time at 1600 Pennsylvania Avenue at first.
She was the subject of numerous headlines earlier this year when it emerged that she was romantically involved with disgraced Trump adviser Rob Porter, who was accused by two of his ex-wives of being physically abusive.
Porter denied the allegations, but resigned under pressure. The Hicks-Porter romance has reportedly since fizzled.
She was the fourth White House communications director since Trump took office, taking over for Anthony Scaramucci, who was ousted after serving in the post for just 10 days.