John Kelly appointment: Trump replaces chief of staff Priebus
US President Donald Trump has named General John Kelly, who currently heads the Department of Homeland Security, as his next chief of staff.
The announcement, made on Twitter on Friday afternoon, removes Reince Priebus from the role.
The embattled former chief of staff had faced pressure since being named as a possible leaker by Mr Trump's newly appointed director of communication.
Mr Priebus told CNN he resigned on Thursday after talking with Mr Trump.
"The president wanted to go in a different direction," he told CNN's Wolf Blitzer, adding that he thought Gen Kelly was "a brilliant pick".
Anthony Scaramucci, who was appointed communications director one week ago, had accused Mr Priebus - a Republican Party stalwart - of leaking to the press.
He also phoned a reporter to unleash a profanity-filled rant against Mr Priebus, whom he called a "paranoid schizophrenic".
Gen Kelly is a retired general who has become the face of border security.
In a series of tweets just before 17:00 (22:00 GMT) on Friday, the president praised the former Marine Corps general as a "great American" and a "great leader".
"John has done a spectacular job at Homeland Security. He has been a true star of my administration," said the president.
He will start work on Monday, a White House spokesperson says.
Gen Kelly's deputy, Elaine Duke, will become acting head of the Department of Homeland Security.
Glittering career of John Kelly
- the former four-star general had a military career spanning four decades
- he is the highest-ranking military officer to lose a child in the wars in Iraq and Afghanistan
- son Robert, a first lieutenant in the Marines, was killed in combat when he stepped on a landmine in Afghanistan in 2010
- at Homeland Security, was responsible for border, immigration, cyber hacking, airport security and natural disaster management
In a third tweet, President Trump praised the outgoing chief of staff, who had previously worked as the chairman of the Republican National Committee (RNC).
"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," he said.
In his previous role as RNC chairman, he acted as a bridge between the Republican nominee and a party establishment that was often uncomfortable with its own presidential standard-bearer.
Analysis: Trump cutting Republicans loose
By Anthony Zurcher, BBC News, Washington
Was there really any doubt who Donald Trump was going to side with in the Priebus-Scaramucci feud?
The newly appointed communications director took dead aim at the chief of staff online and on-air this week, calling him a "paranoid schizophrenic".
Well, as the saying goes, even paranoids have enemies. On Friday afternoon the axe fell.
With Priebus's departure, the purge of establishment Republicans within the Trump White House is in full swing. The former head of the Republican National Committee was brought in as a veteran Washington player to help bridge the insider-outsider gap in the administration, but instead he tumbled into the chasm.
It's clear, in tweets and comments, that Mr Trump believes the Republican Party does not have his best interests in mind. Now he's cutting the party loose.
By all accounts Priebus's successor, John Kelly, is a well liked, highly respected man. His selection is yet another example of Mr Trump's preference for military brass in positions of authority.
His managerial skills will be sorely tested, however, by a White House staff that has been wracked by internal strife. Leading an army into battle may seem easy by comparison.
White House spokeswoman Sarah Sanders said she did not think the administration's relationship with the Republican Party would be affected by Mr Priebus's exit.
"I think we've still got a good relationship. We're going to continue working with the party and doing what we came here to do," she said.
House of Representatives Speaker Paul Ryan, a close friend of Mr Priebus and a fellow Republican, said he had served "the president and the American people capably and passionately".
"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," he said.