Trump, in a post on Truth Socia on Fridayl, said he would nominate retired Lieutenant General Dan "Razin" Caine to succeed Brown. A former F-16 pilot, Caine was the most recently associate director of military affairs for the Central Intelligence Agency.
Trump will also replace the head of the US Navy, a position held by Admiral Lisa Franchetti, as well as the air force vice chief of staff and judge advocates general for the Army, Navy and Air Force, the Pentagon said.
The decision sets off a period of upheaval at the Pentagon, which is already bracing for firings of civilian staff, a dramatic overhaul of its budget and a shift in US military deployments under Trump's new America First foreign policy.
While the Pentagon's civilian leadership changes from one administration to the next, the uniformed members of US armed forces are apolitical, serving the policies of Democratic and Republican administrations.
Brown, who became the highest ranking military officer in October 2023, had been expected to serve through September 2027.
Trump did not explain his decision to replace Brown or say whether he would remain in the job until his successor is confirmed by the Senate.
"I want to thank General Charles 'CQ' Brown for his over 40 years of service to our country, including as our current Chairman of the Joint Chiefs of Staff. He is a fine gentleman and an outstanding leader, and I wish a great future for him and his family," Trump wrote.
Reuters was first to report planning by the incoming Trump administration in November to carry out the sweeping firings, including Brown.
Defence Secretary Pete Hegseth had been sceptical of Brown before taking the helm of the Defence Department with a broad agenda that includes eliminating diversity, equity and inclusion initiatives in the military.
In his most recent book, Hegseth asked whether Brown would have gotten the job if he were not Black.
Brown, a former fighter pilot who was only the second Black officer to become chairman of the Joint Chiefs of Staff, recounted his experiences in an emotional video posted online after the 2020 killing of George Floyd.
He was on official travel when Trump made the announcement. Hours before Trump's post, Brown's official X account had posted images of him meeting troops on the US border with Mexico.
"Border Security has always been critical to the defence of our homeland. As we navigate unprecedented security challenges... we will ensure our troops at the border have everything they need," he said in a post on X.
A spokesperson for Brown did not immediately respond to a request for comment.
