News networks began calling the race for Mr Trump as early as a half-hour after the caucuses began.
Mr Trump, flanked by his sons Don Jr and Eric, gave a victory speech Monday evening.
"I really think this is time now for everybody to come together, whether it is Republican or Democrat or liberal or conservative, it would be so nice if we could come together and straighten out the world and straighten out the problems and all of the death and destruction that we're witnessing that has practically never been seen," he said. "I want to make that a big part of our message, we're going to come together."
He then turned his attention to his rivals.
Mr DeSantis and Ms Haley are largely considered Mr Trump's only serious opposition, as they've been the only GOP candidates capable of breaking double digits in polling.
He offered the pair a bizarre kudos for "having a good time together."
"I want to congratulate Ron and Nikki for having a good time together," Mr Trump said during the speech. "They had a good time together, and I think they both actually did very well, we don't even know what the outcome of second place is."
Businessman and GOP primary candidate Vivek Ramaswamy also received a nod from Mr Trump during the speech.
"I also want to congratulate Vivek, because he did a hell of a job, he came from zero and he's got a big percent, probably almost eight per cent, and that is an amazing job," Mr Trump said. "Very smart people, very capable people."
Mr Trump won the Iowa Caucus with 51 per cent of the vote, according to The New York Times.
Following the victory, Mr DeSantis took a page from Mr Trump's playbook and accused news outlets of engaging in election interference to support the former president.
"It is absolutely outrageous that the media would participate in election interference by calling the race before tens of thousands of Iowans even had a chance to vote,"Mr DeSantis's communications director Andrew Romeo said. "The media is in the tank for Trump and this is the most egregious example yet."
Ms Haley has responded to her first major loss of the campaign season by insisting she will no longer participate in debates unless Mr Trump participates as well.
Mr DeSantis sneered at the ultimatum, and insisted Ms Haley was just vying to be Mr Trump's running mate.
“The reality is that she is not running for the nomination, she’s running to be Trump’s VP,” Mr DeSantis posted to X/Twitter on Tuesday. “I won’t snub New Hampshire voters like both Nikki Haley and Donald Trump, and plan to honor my commitments. I look forward to debating two empty podiums in the Granite State this week.”