With his legislative agenda largely stalled, Trump became convinced that Priebus was a "weak" leader after being lobbied intensely by rival advisers to remove the establishment Republican fixture who has long had friction with some of Trump's inner-circle loyalists, according to White House officials.
Kelly's hiring is expected to usher in potentially sweeping structural changes to the turbulent operation. Kelly intends to bring some semblance of traditional discipline to the West Wing, where warring advisers have been able to circumvent the chief of staff and report directly to the president and sidestep the policy process, according to people with knowledge of his plans.
Kelly, a retired four-star Marine general, earned Trump's approval for his work combating illegal immigration and his leadership qualities, both in the battlefield and at the Department of Homeland Security, according to White House officials, who said the president been talking about replacing Priebus with Kelly for the past few weeks.
"He is a Great American and a Great Leader," Trump tweeted. "John has also done a spectacular job at Homeland Security. He has been a true star of my Administration."
The president added, "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!"
The announcement comes after deep personal animus between Priebus and Anthony Scaramucci, newly appointed as White House communications director, burst into public view Thursday when Scaramucci accused the chief of staff of leaking damaging information about him to the news media and savaged Priebus in a profanity-laced interview with The New Yorker.
Priebus said in a statement, "It has been one of the greatest honors of my life to serve this president and our country. I want to thank the president for giving me this very special opportunity. 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."
Allies to Priebus said he told them he had resigned on Thursday, concluding that the internal chaos would only escalate. One Priebus friend said the chief of staff had described the situation as "unsustainable," saying he felt demeaned by the president's treatment of him and was frustrated that he could not assert control over basic White House functions, such as policy development, communications and even White House announcements -- which sometimes were made impulsively by the president, such as this week's announcement to ban transgender people from serving in the military.
But some White House officials said the decision for Priebus to depart was made by Trump, and that the president forced him out on Friday. These officials noted that Priebus presided over the Friday morning senior staff meeting and accompanied Trump to a law enforcement event in New York.
Regardless, his final departure was a humiliating coda for what had been a largely demeaning tenure during which Priebus endured regular belittling and emasculation from rival advisers -- and even, at times, the president himself.
When Air Force One touched down Friday afternoon at Andrew's Air Force Base, Priebus, senior policy adviser Stephen Miller and social media director Dan Scavino all loaded into a Suburban. But moments later, Miller and Scavino hopped out of the vehicle, and as word trickled out about the chief of staff's ouster, reporters inched close to snap photos of Priebus, who sat alone on the rain-soaked tarmac. Priebus' vehicle then pulled out of the presidential motorcade, which proceeded along to the White House without him.
"I think any observer -- including one that did not speak English and knew nothing about politics and came from another planet and solar system -- could, after observing the situation in the White House, realize the White House is failing," said one informal White House adviser, who spoke on the condition of anonymity to share a candid assessment. "And when the White House is failing, you can't replace the president."
Trump has long been drawn to military leaders -- "my generals," he calls them -- and by appointing Kelly, the president hopes to bring military discipline to his often-unruly West Wing. Kelly is expected to be sworn into the job on Monday morning and convene a Cabinet meeting.
Kelly, who is widely admired by Trump family members and loyalists, has formed a bond with the president over recent months that was fortified when he aggressively defended the travel ban policy. Their relationship has only grown stronger since, with Trump telling aides that he sees Kelly as someone who dutifully follows through on his agenda -- including a border security crackdown and sharp reduction in illegal immigration -- and does not cause him problems.
Sarah Huckabee Sanders, the incoming White House press secretary, said of Kelly in a statement, "The entire administration loves him and no one is comparable."
Sanders also commended Priebus for his service. "He was loyal in his dedication to the president," she said. "The president thanks him and his family for his great service to the country, and he will always be a member of the Trump Team."
Priebus, who as chairman of the Republican National Committee nurtured a close relationship with Trump during last year's campaign, was named White House chief of staff to bring Washington experience to the administration of a political novice.
Part of Priebus' pitch for the job was that he could use his long-standing relationships with Republican leaders on Capitol Hill - including House Speaker Paul Ryan, R-Wis., a personal friend - to help pass Trump's ambitious agenda, including major legislation on health care and taxes.
But Priebus became consumed by internal battles, clashing not only with Scaramucci but finding himself under siege by Trump advisers inside and outside of the White House who complained that he was ineffectual and more concerned with his own public image than the president's.
After Scaramucci was named communications director last week against Priebus' vehement objections, White House officials widely believed that Priebus' position had become more imperiled.
Rumors of Priebus' firing have circulated for months now. As one senior White House official put it, there was a "phony death march for six months." But the dynamic changed over the past 10 days or so.
"It reached a fever pitch of the president complaining about Reince to all of us," said this official, who requested anonymity to speak candidly. "If we heard it once, we heard it 20 times in the last week - this erosion of confidence. The word was 'weak' - 'weak,' 'weak,' 'weak.' 'Can't get it done.'"
Trump's own family had soured on Priebus at least several weeks prior. Jared Kushner, the president's son-in-law and senior adviser, had been telling associates he believed Priebus was doing a poor job and running the White House ineffectively - a view that both Ivanka Trump, the president's daughter and adviser, and first lady Melania Trump also privately conveyed to the president.
Any negative mention of Priebus in a news story - even a single sentence or mere clause - would often elicit frantic phone calls from the more junior staffers reporting directly to him, the sort of vigorous defense in the media the president came to believe was not afforded to him. The impression within the White House - that Priebus was most concerned with defending his own image - further undercut his standing with Trump and the president's family.
Both Kushner and Ivanka Trump were supportive of Priebus' departure Friday, but also expressed admiration for Kelly, according to an administration official.
Ryan issued a statement praising Priebus, saying he "left it all out on the field, for our party and our country."
"He has achieved so much, and he has done it all with class," Ryan said. "I could not be more proud to call Reince a dear friend."
On Friday, as Trump traveled to New York, he took both Scaramucci and Priebus on Air Force One with him.
Asked to comment on the changes, Trump told reporters traveling with him that Priebus is a "good man," and that Kelly is "respected by everybody."
Kelly has a warm rapport with White House chief strategist Stephen Bannon, who has worked closely with him on shaping the administration's border enforcement policy. They have built a connection over their families' military service. Bannon, a former Navy officer, has a daughter who graduated from the U.S. Military Academy at West Point.
Kelly is also well liked by Kushner, who sees him as a stable presence with a low key personality. He has described Kelly to associates as the kind of figure he'd like to see have more say in the administration.
Kelly's reputation and ability to work with both wings of a warring West Wing made the decision easier for Trump, the officials said.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)