Jason Greenblatt, a key architect of President Donald Trump's much-delayed Israeli-Palestinian peace plan, announced his resignation Thursday.
Greenblatt, who worked alongside Trump's powerful son in law Jared Kushner, said in a statement it had been "the honor of a lifetime" to work in the White House.
A senior administration official said Greenblatt was going to spend more time with his family but left on good terms and "holds the confidence of the president."
His departure places another question mark over the troubled plan, which Trump has touted as the "deal of the century," but has yet to see the light of day and has been rejected in advance by the Palestinians.
Just a week ago, Greenblatt signalled the latest pushback to the plan's unveiling, saying it would not be released until after the September 17 Israeli election that will decide whether Trump ally Prime Minister Benjamin Netanyahu stays in power.
Trump has repeatedly boasted that he is the most pro-Israeli US president in history. He has slashed aid to the Palestinians, while making big concessions to the Israelis.
According to the Republican, his vision for ending the Israeli-Palestinian conflict revolves around encouraging massive economic investment. However, Palestinian leaders have dismissed the plan as one-sided and failing to address their wish to end Israeli occupation.
Netanyahu said after news of Greenblatt's departure that he thanked him "for his dedicated work for security and peace and for never hesitating to tell the truth about the state of Israel to its detractors."
Trump tweeted that Greenblatt "has been a loyal and great friend and fantastic lawyer."
However, Hanan Ashrawi, a senior Palestinian official, told AFP: "I think the Palestinians as a whole are going to say good riddance."