Speaking at a news conference here at Trump's private club, Mar-a-Lago, the retired neurosurgeon echoed Trump's recent calls for party unity and pleaded with the GOP to allow the "political process to play out."
"What I've been seeing recently is political operatives ... once again trying to assert themselves and trying to thwart the will of the people," Carson said. "I find that to be an extraordinarily dangerous place right now."
Carson's endorsement, coming just one week after he ended his own White House campaign, gives Trump a significant boost as the Republican nominating contest heads to critical states like Florida and Ohio on Tuesday. Trump said he did not make any promises to Carson about a future role in a potential Trump administration, but pledged that Carson would play a "big, big part" in his campaign.
Carson -- whose campaign and demeanor were polar opposites of Trump's in many ways -- played the role Friday of vouching for Trump's character and integrity. He explained that there were "two Donald Trumps" -- one that the public sees, and another more reserved and "cerebral" man who "sits there and considers things very carefully."
"Some people have gotten the impression that Donald Trump is this person who is not malleable, who does not have the ability to listen, and to take information in and make wise decisions. And that's not true," Carson said. "He's much more cerebral than that."
Carson became the second former presidential candidate to back to Trump. New Jersey Gov. Chris Christie endorsed the businessman two weeks ago.
Earlier this week, Carson had indicated that he would be open to backing either Trump or Ted Cruz. Carson and Cruz's relationship hit a rocky patch around the first GOP primary contest in Iowa, when the Cruz campaign incorrectly told precinct captains while the caucuses were taking place that Carson may be dropping out of the race. Carson called on Cruz to take responsibility and fire whoever was responsible for the "blatant lying," and Cruz subsequently apologized.
On Friday, Carson -- a Seventh Day Adventist -- insisted that he had no lingering hard feelings towards the Texas senator.
"I have completely forgiven him. That's a duty one has as a Christian," he said.
On the tense exchanges that he has had with Trump this cycle, Carson said all of that was also history. "We moved on because it's not about me. It's not about Mr. Trump. This is about America."
Trump praised Carson throughout his press conference.
"Having (Carson's) support, really, it just adds total credence to what I'm trying to do and to what we're all trying to do," Trump said, introducing Carson.
Trump says establishment is coming around
Coming off of an unusually civil CNN Republican debate
on Thursday night that lacked in personal insults and attacks, Trump exuded confidence about the trajectory of his campaign. Fielding questions from reporters for about 45 minutes, Trump said he is hopeful about clinching the nomination by getting 1,237 delegates and avoid a situation in which the nominee is chosen at the Republican convention over the summer. Looking ahead to next week, he predicted that he could defeat Ohio Gov. John Kasich in his home state.
Trump suggested that establishment Republicans are beginning to rally around him in private conversations. He once again said he had a respectful conversation with House Speaker Paul Ryan this week, and though he declined to name names, he said he had heard from "virtually everybody in the Republican Party."
One person he has not had contact with: Senate Majority Leader Mitch McConnell. Asked to react to reports that McConnell is planning ways for vulnerable Senate Republicans to distance themselves from Trump should be become the nominee, Trump simply answered: "I'm sure that will change."
Florida Sen. Marco Rubio's communications director seemed to acknowledge that Trump has the best shot at getting the needed delegates to secure the nomination when he said Friday, that Kasich is the best candidate for Republicans who want to defeat Donald Trump in the governor's home state of Ohio.
"If you are a Republican primary voter in Ohio and you want to defeat Donald Trump, your best chance in Ohio is John Kasich," Alex Conant told CNN's "At This Hour with Berman and Bolduan," adding Rubio was the best candidate to debate Trump in Florida.
When asked specifically if he was telling Rubio supporters in Ohio to vote for Kasich, Conant responded, "Yeah, my answer is John Kasich is the one candidate in Ohio that can beat Donald Trump. That's stating the obvious. So ... if you're a Republican primary voter in Ohio, and you don't want Donald Trump to be the nominee, John Kasich is your best bet."
Mitt Romney, the 2012 Republican nominee, has encouraged Republicans to support whoever has the best shot at beating Trump in any particular state so that Republicans could select their nominee at the Republican National Convention in July.