National Security Adviser John Bolton handed in his resignation Tuesday morning at President Trump's request, the president announced on Twitter.
Bolton had clashed with other members of the administration, notably Secretary of State Mike Pompeo, on foreign policy issues.
"I informed John Bolton last night that his services are no longer needed at the White House. I disagreed strongly with many of his suggestions, as did others in the Administration, and therefore," Mr. Trump wrote on Twitter. "I asked John for his resignation, which was given to me this morning. I thank John very much for his service. I will be naming a new National Security Advisor next week."
Bolton swiftly responded to Mr. Trump on Twitter, saying that he offered to resign on Monday night.
"I offered to resign last night and President Trump said, "Let's talk about it tomorrow," Bolton wrote, slightly contradicting Mr. Trump's account that he asked for Bolton's resignation.
Bolton was often at loggerheads with Pompeo, most recently over U.S. negotiations with the Taliban to withdraw American troops from Afghanistan. The two disagreed over whether a reduction of U.S. troops could happen with or without a negotiated deal. Bolton opposed negotiating with the Taliban.
On Saturday, Mr. Trump made the surprise announcement that peace talks with the Taliban had been canceled. Mr. Trump tweeted that he "called off peace negotiations" in the wake of last week's car bomb attack near the U.S. embassy in Kabul that killed one American service member and another NATO soldier, as well as at least 10 civilians.
The president further revealed that the meetings with Taliban representatives and the president of Afghanistan would have been held at Camp David, the presidential retreat in Maryland — on the very week marking the 18th anniversary of the 9/11 terror attacks, in which 3,000 Americans died on U.S. soil.
Bolton, who served in the George W. Bush administration and was a supporter of U.S. engagement in Iraq and Afghanistan, was one of the most hawkish foreign policy voices in Mr. Trump's cabinet. Bolton often advocated for a harder line in dealing with Iran.
Bolton was scheduled to speak with Treasury Secretary Steve Mnuchin and Pompeo Tuesday afternoon.
He is the fourth national security adviser to depart the administration since Mr. Trump took office.