Knight will replace Marc Short, who plans to leave his post as White House legislative affairs director this month. Short has served in the West Wing since Trump’s inauguration.

“I will be forever indebted to President Trump and Vice President Pence for the opportunity to join their campaign in 2016 and be part of an Administration that has worked with Congress to pass the largest tax relief in American history, to rebuild our military with the largest funding increases since the Reagan years, and to confirm more appeals court judges than any Administration in its first two years," Short said in a statement.

John Kelly John Francis KellyMORE White House chief of staffpraised Short as "an integral part of the White House staff."

"He and his team helped the President rebuild the military, pass historic tax reform and achieve unprecedented legislative successes," Kelly said in a statement. "We will miss his profound expertise, commitment to the taxpayers, and leadership."

The transition comes at a pivotal time for the White House, which is gearing up for a fierce confirmation battle with Democrats over Trump’s Supreme Court nominee, Brett Kavanaugh. The fight is also expected to have ripple effects on the November midterm elections.

Knight’s decision to accept the role is somewhat surprising: She announced in June she was leaving the White House to become executive vice president of public affairs at the Clearing House, a financial services trade association and lobbying group.

Before joining the White House, Knight worked in a top public affairs role at Fidelity Investments and as a lobbyist for the Securities Industry and Financial Markets Association. She also worked as a staffer on the House Ways and Means Committee and the Joint Economic Committee during the late 1990s and early 2000s.

Short’s departure also accelerates the record-setting pace of turnover on Trump’s senior White House.

More than 60 percent of Trump’s top-tier aides have left their positions, according to Martha Kumar, director of the White House Transition Project, the highest rate of any recent president.

Updated: 1:49 p.m.