Twenty-eight-year-old interim White House Communications Director Hope Hicks will serve in the role on a permanent basis. The longtime Trump aide is the fourth person to fill the position, replacing Anthony Scaramucci, who was fired in July after just 10 days on the job.
The ex-Trump Organization employee is one of his most trusted aides.
As White House communications director she will be responsible for shaping the administration's message - although in a less visible way than press secretary Sarah Huckabee Sanders.
The appointment of Ms Hicks - a former Ralph Lauren fashion model - comes after a summer of staff shake-ups at the White House.
Mr Scaramucci was fired after he raised eyebrows for calling a reporter to give a profanity-laced tirade against his own colleagues.
President Trump's chief of staff, Reince Priebus, and spokesman, Sean Spicer, both left their posts after Mr Scaramucci's appointment.
General John Kelly, who replaced Mr Priebus, sacked Mr Scaramucci after he was sworn in.
Mike Dubke, who was first appointed as communications director, resigned in May.
Mr Spicer also filled in as communications director while the post was open over the summer.
Can Hicks hope to handle Trump?
By Tara McKelvey, BBC White House correspondent
Reporters say mean things about Hope Hicks. They complain that she's not qualified for the job, and they say she's in over her head.
It's true that she did not come from the Washington establishment or the political world. A former Ford model, she started working for Trump in 2015.
Still, she has something valuable - the president's trust. Among those in the West Wing, she's the closest to Trump and knows how he wants to achieve his goals.
That seems like a good background for someone who's handling his communications strategy.