Donald Trump has named John F Kelly as his new White House chief of staff after sacking Reince Priebus.
The President thanked Mr Priebus for his service, calling him "a good man" who had served his country well.
The two men had travelled together earlier in the day to an appearance in Brentwood, New York.
:: The unpredictable president strikes again
Mr Priebus' future had been put into question earlier on Thursday, when comments made by Anthony Scaramucci - the new White House communications chief - were published in the American press.
During a phonecall with New Yorker reporter Ryan Lizza on Wednesday night, Mr Scaramucci badmouthed the former chief of staff, saying that Mr Priebus had "c***-blocked" and orchestrated leaks against him.
Mr Scaramucci's colourful turn of phrase appears to have been accusing Mr Priebus of obstructing his success in Mr Trump's White House administration.
During the expletive-laden rant , the newly appointed director of communications also rubbished the White House chief strategist, saying: "I'm not Steve Bannon. I'm not trying to suck my own c***".
The slur seeks to imply Mr Bannon places his own interests before those of the White House.
The communications chief is also believed to have had an intense rivalry with Sean Spicer, who resigned as press secretary when Mr Scaramucci was hired by Mr Trump a week ago.
Mr Trump was swift to announce the replacement for his chief of staff, tweeting: "I am pleased to inform you that I have just named General/Secretary John F Kelly as White House Chief of Staff. He is a Great American and a Great Leader.
"John has also done a spectacular job at Homeland Security. He has been a true star of my Administration."
The President also tweeted his thanks to Mr Priebus, writing: "I would like to thank Reince Priebus for his service and dedication to his country. We accomplished a lot together and I am proud of him!"
Mr Priebus said in a televised statement from the White House: "The President has a right to hit a reset button. I think it's time to hit the reset button.
"He intuitively determined that it was time to do something different, and I think he's right...
"I will continue to serve as a strong supporter of the President's agenda and policies.
"I can't think of a better person than General John Kelly to succeed me and I wish him God's blessings and great success."
Speaker of the house Paul Ryan also tweeted a statement, writing: "He has achieved so much, and he has done it all with class. I could not be more proud to call Reince a dear friend."