But Carson stopped short of saying he was officially leaving the race.
The retired neurosurgeon and his aides reached the decision after a staff meeting Wednesday morning in Baltimore following a disappointing finish on Super Tuesday.
In an email to supporters, campaign chairman Bob Dees said the "political efforts must come to a close."
"We have often said that 'reality is our friend.' The reality is that we together have been on an amazing journey -- the right candidate for the right cause for the right reasons at the right time," Dees wrote.
"No doubt many of you have tears as you read this, just as I tearfully write these words -- tearfully because the reality is that our political efforts must come to a close," he added. "Gratefully, the grass roots movement that has given new voice to 'We the People' and has inspired millions will continue."
Carson said he will go into more detail during an appearance at the Conservative Political Action Committee Conference near Washington on Friday.
It appears to end what once seemed like a promising campaign for the first-time political candidate. He was the first GOP candidate to overtake Donald Trump in the polls for a period of several weeks around October. But as fall turned to winter, Carson consistently lost ground to Trump and later Texas Sen. Ted Cruz.
Armstrong Williams, Carson's business adviser, said it is clear that Trump has things wrapped up.
"Everyone needs to come to the realization that Donald Trump will be the nominee when it's all said and done," Williams said in an interview. "And that's the reality. I know they're saying they have the best chance of toppling Trump, but let's admit it, they have no pathway either. And every event, let's admit it, Trump has done well. ... Since Iowa, he has been steamrolling."
Williams also insisted Carson will back the GOP primary winner. "Dr. Carson will support the eventual nominee," he said.
Bumpy road on the campaign trail
Carson never made a cogent argument for his candidacy, running mostly on his biography rather than policy and political views. Carson undisputedly had an impressive personal story to tell. He overcame a troubled youth in inner-city Detroit, becoming a star student and eventually a world-class neurosurgeon. He won international acclaim in the late 1980s after successfully separating conjoined twins.
In June 2008, President George W. Bush awarded Carson the Medal of Freedom, the nation's highest civilian award. "For a time, young Ben Carson was headed down that same path," Bush said at the time. "Yet through his reliance on faith and family, he turned his life into a sharply different direction."
But Carson's origin story took a hit after a CNN report raised questions
about claims he made about violent episodes as a youth. Trump, rising in the polls, took to mocking Carson
, particularly over a story from the surgeon's memoir about Carson attempting to stab a friend -- the knife broke in a half after hitting a large belt buckle.
Carson's debate performances didn't help, either. He often seemed halting in his speech patterns in a forum that prizes quick and snappy soundbites. And his command of policy appeared shaky -- he asserted that the Chinese were in Syria, a claim the White House disputed. He repeatedly deflected questions on how to confront ISIS, among other foreign policy challenges. Even on health care, Carson's seeming specialty, he didn't have many specifics to offer beyond saying that Obamacare should be abolished.
Carson's campaign also suffered internal conflicts, with competing power centers often at odds. In the run-up to the Iowa caucuses, a contest that was crucial to his chances because of his connections with evangelicals, the tensions came to a head, with his top advisers leaving the campaign. Adding to the turmoil, Carson's former advisers were unusually public in their criticism of Carson as a candidate and of his campaign structure.
When voting actually began with the February 1 Iowa caucuses, Carson wasn't much of a factor except as a spoiler. He finished fourth at 9.3%. His New Hampshire primary showing was even worse. Carson finished eighth, with only 2.3% of the vote -- ahead only of candidates who had dropped out of the race but whose names remained on the ballot. Then in the February 20 South Carolina primary, Carson finished sixth, with less than 8% of the vote.
Running for Senate?
Republican operatives, looking to move Carson out of the race as they try to remove obstacles to finding a challenger to Trump, were planning Wednesday to suggest he drop out and instead run for the U.S. Senate seat in Florida
John Philip Sousa IV, who operates the 2016 Committee, a pro-Carson super PAC, said he has not spoken with Carson but would be intrigued by the possibility of a Senate race.
"Would he be a great U.S. senator? Absolutely. Would we support him all the way? You bet we would," Sousa said in an interview.
Sousa suggested the super PAC could back one of the other GOP candidates should Carson endorse one. Another option would be to convert "into an anti-Hillary super PAC, which we could easily do and which we believe our supporters would be very excited about," to attack the Democratic front-runner Hillary Clinton.
For his part, Williams said he thought the Florida concept is a non-starter.
"Isn't it flattering that people in Florida think so highly of Dr. Carson that they would want him to run for Senate seat in Florida? I think they wanted him to run in Florida because they wanted him out of the race," he said.
"I don't need to advise him on that because I already know that he has no interest in that. Remember, they also tried to get him to do the same in the state of Maryland, this is not the first time he's been approached about this."