Donald Trump's top economic adviser Gary Cohn is set to resign.
He follows the US president's close aide Hope Hicks in becoming the latest high-profile departure from the White House.
Mr Cohn, a former president of Goldman Sachs, said it had been "an honour to serve my country" in a statement.
He played a key part in helping Mr Trump push through his sweeping tax reforms, but rumours have repeatedly suggested the pair were not close.
His departure date has not yet been set but it is likely to be within a few weeks, the White House said.
"It has been an honor to serve my country and enact pro-growth economic policies to benefit the American people, in particular the passage of historic tax reform," said Mr Con.
"I am grateful to the President for giving me this opportunity and wish him and the Administration great success in the future."
The director of the National Economic Council has been the leading internal opponent to Mr Trump's planned tariffs on imports of steel and aluminium, working to orchestrate an eleventh-hour effort in recent days to get the president to reverse course.
But Mr Trump resisted those efforts, and reiterated on Tuesday he will be imposing tariffs in the coming days.
Mr Cohn's departure comes amid a period of unparalleled tumult in Mr Trump's administration and aides worry that more staffers may soon head for the doors.
The announcement came hours after Mr Trump denied there was chaos in the White House.
The president maintained that his White House has "tremendous energy," but multiple White House officials said Mr Trump has been urging anxious aides to stay.
"Everyone wants to work in the White House," Mr Trump said during a joint press conference with Swedish Prime Minister Stefan Lofven. "They all want a piece of the Oval Office."
Mr Cohn nearly departed the administration last summer after he was upset by the president's comments about the racial violence in Charlottesville, Virginia. Mr Cohn, who is Jewish, wrote a letter of resignation but never submitted it.
"Citizens standing up for equality and freedom can never be equated with white supremacists, neo-Nazis, and the KKK," Mr Cohn told The Financial Times at the time.
"I believe this administration can and must do better in consistently and unequivocally condemning these groups and do everything we can to heal the deep divisions that exist in our communities."
