She was not well liked by some White House advisers, including Reince Priebus, the former chief of staff; Jared Kushner, the president’s son-in-law and senior adviser; and Mr. Kelly, according to multiple White House officials. Early in his tenure, Mr. Kelly identified the public liaison office as a major problem that he had to contend with, but it took months to move Ms. Newman to it, these people said.

It is not unusual for presidential appointees to leave after the first year of an administration. Other members of Mr. Trump’s administration have already left or were asked to resign amid controversy.

Armstrong Williams, a conservative media personality and business owner, said that he spoke to Ms. Newman on Wednesday morning and that she sounded both “torn” and “relieved.” Ms. Newman told Mr. Williams she had not been fired — she wanted to leave.

Ms. Newman was known among staff members as a disruptive force who intimidated a number of Trump aides, before the arrival of Mr. Kelly. But Mr. Williams said that Mr. Trump was so fond of Ms. Newman that she once could walk into the president’s office whenever she wished. That practice ended for her and other White House aides when Mr. Kelly became chief of staff in late July. However, Mr. Priebus had barred Ms. Newman from several White House meetings. And several people familiar with Ms. Newman’s departure said she had been sending articles to Mr. Trump without Mr. Kelly’s approval.

Ms. Newman appeared in the first season of “The Apprentice,” in 2004, and worked on Mr. Trump’s 2016 presidential campaign. On Wednesday night, the president tweeted her a note of encouragement: “Thank you Omarosa for your service! I wish you continued success.”

At the White House, she mostly maintained a lower public profile. When she was preparing for her wedding, Ms. Newman told other White House advisers that she planned to ask Mr. Trump if she could have a reception in the building in her honor. When reporters learned of the plan, she abandoned the idea. But she did show up at the White House after her wedding with members of the wedding party, according to a person familiar with the events.