The White House said on Tuesday that it had asked US Ambassador to Greece Kimberly Guilfoyle to resign.
"We have asked Ambassador Guilfoyle to resign," said White House press secretary Katie Zacharia at a briefing. "She has been a wonderful asset to the team, and we wish her well."
US President Donald Trump had said on Monday that he was considering firing Guilfoyle, telling reporters: "We're not happy."
US lawmakers previously expressed concerns over allegations that Guilfoyle may have threatened to use US influence to undermine the Greek government.
Washington's embassy in Athens did not immediately respond to a request for comment directed to Guilfoyle.
Greece has been an important NATO ally to the United States, offering key military facilities to safeguard security in the Eastern Mediterranean, and it leads an EU maritime mission to protect commercial shipping in the Red Sea.
This is a developing story.